Sounds tough, because of her past. Until the counsellors and pediatricians can devise solutions, what have you tried?
Is she willing to recognize, that it's quiet time in the home? Does she prefer the door, open or shut? Nightlight on or off? Can she be trusted to be allowed to stay awake but confined to her room? Would a tv with one movie continuously playing work?(not a big fan of tvs in bedrooms, but she seems like she may have terrors of the night?) Classical music? What works? What doesn't?
A catch phrase for me, at one point with one of my sons, thinking my oldest, is I will see you after the sun comes back out. The word morning is a tough concept for children, sometimes. I told him repeatedly this is quiet time. Not play time.
Her body will not be able to withstand such lack of sleep. There's a huge part of her trigger. Are there other parts of your home she'll fall asleep? A couch, to carry, where she wakes up, in her own bed, adjusts her to realizing it's safe there?
There's adjustments that can be taken to get her back on track. Is she in communication with her mother? Do you talk with her about her? Asking to understand if that glimmer is working against her viewing your home as where she's going to be for a long time in her childhood.

In addition, had my son's friend many overnights plus, two whole weeks. He informed me, he doesn't sleep through the night. I said, I don't always either, but I have the sun rule. He sometimes talked in his sleep, but he slept just fine. I offered him a safe haven.