From my experience of multi-month insomnia caused by stress, the only thing that has short-circuited sleep deprivation consistently is exercise and exposure to sunlight throughout the day.
Early morning, vigorous exercise would force your DD to wake and build a natural sleep cycle again. If she spends most waking hours with exposure to direct sunlight, and consumes a high-protein diet (especially foods high in tryptophan later in the day), these will provide natural support to her circadian rhythm. It will take some short-term pain, though. I found daily exercise was what was needed, and there was a period of about 2 weeks where I had to force through some pretty extreme exhaustion to naturally fall asleep within 20 minutes at a desirable time.
