I am wondering if this is beyond us and hopeless. I would like to know if you have any thoughts on this. As I always recommend, follow your instincts and good common sense as to whether she needs more help than you are able to give her. Make sure she is getting the therapy she needs. I am not familiar with the foster care system, but I am assuming that it sees to it that they are getting emotional help on top of a new placement.
Children can spot phony adulation and syrupy words instantly.
What you will need to do is give her space to adjust, which I am sure you already know. Often the love in such a child or person has been neglected, disbelieved, abused and denied. A child like this probably doesn't know what honest, unconditional love is all about. You need to let her get acclimated to her new surroundings and try very hard not to buck horns with her. I am sure that is what she is used to.