What Causes Disturbed Sleep?

My daughter age 20 has had problems sleeping. She lives at home and is attending college with a light load- 12 credits and works about 6 hrs/week as a direct line therapist with autistic children. She has irregular sleep problem and says she has trouble falling asleep. She will go to sleep at 5.00AM and sleep until 3-4.00PM at times. We can get her back sometimes on a regular schedule when needed for classes but it is hard for her to adjust. She has missed classes due to oversleeping at times.

Thank you,
DF