A good thing!
How old are you people? Not that chronological age always lines up perfectly with emotional maturity, but your girl seems a bit... childish, if that is an English word. And it would make a world of difference whether she is 20 or 30 years old in exhibiting these behaviors and reactions. She might be having a personality and/or mood disorder, or she might just be very very young. Whatever it is, I think you are taking the right steps in stopping the dating and seeking out help for her.
And yes, pets/additional foster children are a bit hazardous at this point, after reading the full back story. Trust TruckerPete; bringing in more live beings to be taken care of will just mean more work for you.
What your fiancee is lacking in her life and what she is trying desperately to find is not more love; it's more self-love.
Me: bi female in my twenties