not sleeping in her room.

Lately Aelita has been refusing to sleep in her room and it's getting really fustrating. She was doing so well when we first got their new beds but now she keeps saying that she's scared. how can i get her to sleep in her own bed again? right now i have kiana's old crib mattress on my floor for them to sleep on when they get scared but with Aelita it's every night and she won't even stay on the mattress and often ends up in my bed by morning.