You might check into sleep apnea. I spent about 15 years getting progressively worse at sleeping. Finally my therapist suggested a sleep study and I have severe obstructive sleep apnea. So a CPAP machine was a lifesaver. I sleep much better now. It does take a while to get used to if that is the problem but it's worth it.
Does she snore or have you noticed her stop breathing from time to time when sleeping? If you stop breathing, your body eventually will wake you up to get you breathing again.
Just a thought.
