Awaken by salvia in throat and choking

It has been over a year now, and our daughter will be woken up almost choking on her salvia. She gets up and gets a towel too wipe the excessive drool coming out of her mouth. It is clear salvia  and she has had a sleep study and it shows normal. We have also tried the reflux meds but it is still happening. She is diagnoised with complex partial seizures and has been taking the depakote er for 5yrs. Any direction on what too do would greatly be appreciated.