Wow, we know she is sleeping, we just don't know when. Is she irritable? If not, she is getting enough sleep. So now the problem is safety.
I would consider having activities that she can do in her bed when she wakes up. Colorforms, crayons and paper, a snack, a flash light, a tape with ear phones she can listen to. There have to be rewards for staying in the room, consequences for leaving the room without an adult's permission. Even put a potty chair in there if you think she gets up to urinate.
If she is cranky, irritable- we all know that tired cry-then you need to seriously consider pediatric benadryl. But first I would have her evaluated by her pediatrician and discuss with him alternatives. With adults, a disturbed sleep pattern can be reestablished with something like benadryl over 3 or 4 days and then withdrawn.
Did this just start when she moved in with you? A conversation about the fears that may interrupt her sleep may also be warranted.
Good luck,
K.