My(M30) GF(F32) is starting to hangout with a mentally unstable, promiscuous friend and I'm concerned. Is this insecurity or a reasonable concern?

So she has this guy that has been a friend of her for many years. He now gets a new girlfriend (we will call her Ana). And Ana has cheated on her boyfriend at least twice, that we know of, as she has confessed. Ana and her boyfriend have a complicated relationship with physical fights, she kinda has mental issues and family problems, long story.

And now I noticed she's using my girlfriend for emotional support and hanging out and I am concerned, because I've personally known cases, in plural, of a single or very hookup-minded female friend that starts hanging more and more with someone else's girlfriend and well, one of these cases ended in confirmed cheat and divorce and the others, we heard things but nothing confirmed.

Like I said, this Ana is unstable, mentally ill and promiscuous, and I don't like that my girl hangs out with her. I haven't brought up this matter to her because I don't want to appear possessive, but neither I want Ana to drag my girlfriend into a sordid situation, or worse.

Do you think am I exaggerating and being insecure?