My girlfriend and I stick to group chats with couples and unicorns and only play together currently (also something we communicate upfront with others).

I got a Snapchat from a younger single girl we met on Feeld and had already established a group chat with, we had yet to play with her and only chatted sporadically with intent to make plans. Before opening the message I went to my girlfriend to let her know she messaged me outside of the group chat and opened it in front of her. It was a picture of her nude in a tub. Of course, girlfriend is understandably upset and confused why it wasn't shared in the group. I offered to remind her that we prefer to keep things in the group chat (which I did send in a message while in front of GF), but my girlfriend began saying she wasn't interested at all in this girl anymore, saying she was too young, she was only going along with my interest in her etc.

I always try to follow my girlfriends lead even when she changes her mind, and she was clearly feeling alot of jealousy and frustration. I offered to disconnect and block the other girl if thats what girlfriend wanted and was met with the deadly "do whatever you want to do" statement. I immediately went to block the other girl to satisfy girlfriends comfort, and as I was doing so the other girl messaged apologizing for crossing the boundary (it is likely that she forgot that we don't chat solo right now).

This led to a long conversation with me providing as much reassurance to my girlfriend as I could, she also felt bad for "removing an opportunity" and felt guilty for feeling jealous in the first place. She eventually admitted that she overreacted and a harmless reminder for the other girl might've been all that was necessary.

What would you do in this situation? How could this have been handled differently?