Oy. She's young, immature, high maintenance, and the whole thing seems like one hot mess.
In addition, I think your reactions and some of your statements don't really sound like you would actually be okay with her having other relationships. It sounds like you really wouldn't be happy in a poly situation with her.
It will hurt for a while, but it seems the best thing for you right now is to walk away. I say dump her and move on.