I think that you should talk to your parents about her and maybe also her therapist. Has she had episodes like this before? the acting out when she was at your house may be because of a feeling of abandonment that she may unconsciously have. She may have repressed memories of her biological mother and father giving her up. The acting out may have been a defense mechanism (an unconscious act/behavior that reduces stress). Or it could be something completly different. I would talk with your parents to see if she has had episodes such as this before and then alert her theapist to the behavior that she demonstrated.
Hope every thing works out,
Jason