Some observations from my latest read:

1. Cersei asks three questions, but gets six answers

Maggy tells Cersei that “three questions may you ask”, but that “you will not like my answers.” Yet the answers she gives are not all in response to questions Cersei actually asks.

The first question Cersei asks is: "When will I wed the prince?" The answer is “never”. However, Maggy then takes it upon herself to answer a second, unvoiced question: “who will I marry?” The answer is “the king.”

The second question Cersei asks is: "I will be queen, though?" The answer is: "Aye. Queen you shall be...”. But then Maggy goes on to answer another unasked question, something like “how long will I be queen?” The answer, of course, is: " . . . until there comes another, younger and more beautiful, to cast you down and take all that you hold dear."

The third question Cersei asks is: "Will the king and I have children?" Here, the answer is interesting. Cersei and the king she marries have no children together, but Cersei doesn’t actually ask that question, so Maggy’s answer is correct given what was asked: "Oh, aye.” Maggy then answers the third unasked question: "how many children will we have?" Six-and-ten for him, and three for you."

2. The answers to the questions Cersei actually asks are straightforward and true on their face

“Never”, “Aye”, “Oh. Aye” or no, yes, yes.

3. The answers to the additional questions are not

The answers to the first and third questions make sense in hindsight, but at the time Cersei was “puzzled” by the answer “the king”, and the six-and-ten “made no sense”. The second is still an open question, but it is destroying Cersei. Maggy gave the answers she wanted to give, notwithstanding the questions, and it is these, or the reality of experiencing them, that she doesn't like (her marriage to Robert is dreadful, he has lots of bastards...)

4. The valonqar prophecy was not in answer to a question

“The old woman was not done with her”. Despite having answered all Cersei’s questions, and some of her own, Maggy goes for an additional information dump:

Gold shall be their crowns and gold their shrouds," she said. "And when your tears have drowned you, the valonqar shall wrap his hands about your pale white throat and choke the life from you."

Maggy is not answering anything here. She is offering unsolicited information, some of which appears to be unrelated to the questions Cersei asked/ Maggy wanted Cersei to know this stuff and volunteered it.

5. The valonqar prophecy is at least partially metaphorical

There was some discussion on the main reddit about how the prophecy was pretty straightforward and literal, but that is only partially true. The, ‘answers’ are straightforward, but these bonus parts arn't. Certainly, ‘gold crowns’ could literally mean the children all take a turn wearing a gold crown, but it is very unlikely that they would literally have golden shrouds. Cersei knows what a shroud is, and relates it to death, but nowhere in the Westerosi funeral rights we have seen one used, and no way would Cersei have let Joffrey have one given the prophecy. Interestingly, on the three occasions “shroud” or “shrouding” is used in the books, it is in the sense of hiding something. Also, Cersei is not going to literally drown in tears (a dose of tears of Lys doesn't drown you but rots your bowels).

Relevantly. Cersei sees the prophecy as literal:

The valonqar shall wrap his hands about your throat, the queen heard, but the voice did not belong to the old woman. The hands emerged from the mists of her dream and coiled around her neck; thick hands, and strong.

Which makes it much more likely that this part actually is metaphorical.

6. Maggy’s words narrow the field, but not a lot...

It is sometimes said that if the valonqar isn't Jaime or Tyrion, it could be "any little brother". But that's not correct. Maggy says the valonqar, not a valonqar, and not your valonqar. The use of ‘the’ here could just be GRRM is trying to make Maggy sound exotic or dramatic, but I doubt it:

“The” is the only definite article in English. You use "the" when you think the person you are speaking to knows what you are talking about, usually either because:

• What you are referring to is uniquely identifiable, either because there is only one, or only one in that context; or
• You have already mentioned or identified it.

Assuming Maggy used “the” intentionally, she is assuming Cersei knows, or will know in context, who she is referring you. This has some interesting consequences for who the valonqar could be.

Who cold Cersei identify from context as the little brother - and here I will assume that Maggy wanted Cersei to stew on it, so it could be someone identifable with later information?

Jaime would not usually not be referred to as the little brother. Even assuming "little" means younger, and younger includes the second born twin, Cersei has two younger brothers. But there are two catches. The first is that Tyrion may be a Targaryan The second is that Jaime was actually mentioned in the discussion. I look at this at the end.

Tyrion can be “the” little brother if discount Jaime because he is a twin. Tyrion is also little because of his physical stature, and possibly because he is a lot younger. Tyrion is actually referred to as Cersei’s valonqar by a Tyroshi merchant in Cersei VIII:

He laid his hand upon his chest. "I bring you justice. I bring you the head of your valonqar."

But Cersei thinks it is Tyrion, and Maggy presumably wants her to think it is Tyrion, and therefore she is probably wrong (although it would be ironic, and very Cersei-ish, if this were the one time she was right).

Sandor is an obvious little brother, but a less obvious cause of Cersei's death, particularly by strangulation.

Loras is probably more properly a little brother or the littlest or youngest brother rather than “the little brother”, although you could perhaps interpret it as the "younger Jaime" or "young kingsguard", but it becomes rather tortuous (although interestingly, on the show he was the only younger brother, and Margaery's little brother, but I understand this was because they were determined to cast Dormer).

Similarly the youngest Kettlebacks.

Stannis was probably the little brother at the time of the prophecy (Cersei was about 10 when she visited Maggie and 11 when Renly was born) but won’t be when Cersei is valonqared.

Even allowing for gender-neutrality, Arya isn’t “the” little sibling, only a middle child. She is physically small though, and Cersei may well think of her as the "little sister" (if she thinks of her at all).

Dany would always have been the little sister, although a younger sibling. Jon is arguably “the” little Targaryan brother, having had one older brother and one older sister, and there is possibly Aegon too.

And then, of course, there is Tommen.

Granted, there are thousands of other little brothers scattered around Westeros, but we have to assume it would be someone Cersei would be able to identify. But even doing that doesn’t narrow it down much. So unless Maggy is totally screwing with Cersei, it seems more likely she is using “the” in the context of someone already referred to in the conversation.

7. The valonqar is more likely someone referenced in the conversation

So what about the second use of "the" - you have already mentioned or identified it?

The entire valonqar prophecy arises in the context of Cersei asking about her marriage and her children. Both the literal answers and the additional answers relate to these things. So Maggy telling Cersei about her death is a non sequitor, unless her death is related to her children.

Looking at the words of the prophecy, the most literal interpretation is that she will be killed by the “little brother” of her children - and that is Tommen: "You marry the king. You have three children. They have gold crowns and gold shrouds. When you are already drowning in sorrow, the younger one kills you."

Chronologically though, it appears Tommen dies first, so Tommen killing Cersei makes no sense unless Tommen either becomes a wight. That sounds kind of ... urgh.. but they *do* strangle, as poor Will discovered in the prologue:

Will closed his eyes to pray. Long, elegant hands brushed his cheek, then tightened around his throat. They were gloved in the finest moleskin and sticky with blood, yet the touch was icy cold.

Cersei refusing to aid in the fight against the dead only to he slain by her wightified remaining child kind of fits (poor Tommen).

On a more tortuous reading, you can dance around the chronology. And while I can't see Tommen strangling his mother (hands chain or no), he could (accidentally) poisons her with the strangling potion.

Another more abstract possibility - and this part of the prophecy is more metaphorical - is that an unborn child kills her.

It is also worth noting that during the conversation they speak of ‘the king’, a reference to Robert, the “the prince”, a reference to Rhaegar, and the YMB one.

8. But what about Jaime?

Even on this analysis, Jaime isn’t totally off the hook, because Cersei has mentioned him too. In reply to the prophecy of about the YMB bringing her down, Cersei says:

"If she tries I will have my brother kill her.”

Hence, “the valonqar” could be a reference to “the little brother who you think will save you will kill you”.

It’s a more torturous connection than Tommen, but not greatly so, and Maggy telling Cersei that Jaime will be responsible for her death rather than her protection is pretty consistent with the other information that Maggy has offered - something Cersei doesn't want to hear, and and that she won't understand until it is obvious.

The interesting thing about this possibility is that Cersei had just confidently stated that if the YMB comes, she’ll “have” Jaime kill her. She says it with confidence - sure he will do it. But we’ve already seen Tyrion certain that Jaime will kill Lancel, and he didn’t. And we know that Cersei is wrong about everything. So what we could have here is the possibility that whoever the YMB rival is, Cersei will assume Jaime will kill her, but he doesn't, and ends up killing Cersei instead. And that would play perfectly into what we know of Cersei, which is generally the opposite to what she thinks will happen happens - and Maggy is flat out telling her as much.

That said, I can’t see Jaime strangling Cersei, he doesn’t have “hands”, and even if he uses the hand chain, it is unlikely to be his (although there are scenarios where it could be). But so much of that passage is potentially metaphorical, even the choking may not be what it seems.