Perhaps provide the parents a copy of your bi-weekly, weekly, or monthly lesson plan and suggest that the parents try to simply introduce the material to the student the night before. The parents are not asked to teach just briefly cover what will be taught the night before. Maybe do one or two sample problems in math or english. She may not miss out on as much then and may even have a head start on some of the problems or worksheets.
Then if she sleeps through some of your lecture she may still have enough to move ahead.
I would also suggest that when teaching and she is awake give it the once over without a lot of extra verbage....explain new concepts with the best quickest examples first.....then go into more detail. If she is still awake great...if not it will give you the opportunity to go on and pick the moment you will disrupt her sleep and not disrupt the whole class.
Place her in the front row near you so that when you do decide to wake her you don't have to go far and the kids eyes will always be forward and not looking back to see if she is asleep or watch her sleep.
Consider putting a tape recorder on your desk or on you and when she falls asleep hit record and ONLY record the Vital material that she is missing.
Reduce the number of problems she has to complete so that if she is awake all of Math period maybe she only is required to do half the number of problems but spends the rest of the time completing the english worksheet she slept through. Maybe have her only spell 1/3 of her sleeping words by writting and the other words she simply picks out the correct spelled work for three. Like
shovel
shoval have her simply circle the correct one (if this takes her less time)
shuval
This issue becomes a matter of making the max use of time...in this case awake time.
Keep in mind that at home this girl is falling asleep all the time so the parents only have so much time to help with school and still have a family life. However providing these additional resources and letting the parents select how much to use and when (as a team approach) may be helpful. With good feedback you can then fine tune what you are doing.
Hope this helps!!!