She may have a post nasal drip.
Hi, welcome to the forum, her symptoms are suggestive of sleep disorder like parasomnias. This condition needs to be differentiated from obstructive apnea.
Few of the individuals are known to suffer from parasomnias esp. when they are on non-benzodiazepine sedatives, drug abuse etc. otherwise no definitive cause exists in few individuals apart from stress, positive past history of abuse etc.
The associated symptoms with the following disorder are confusional wakefulness, sleep paralysis, nightmares and night terrors. This can occur in any sleep stage (REM and non-REM stage).
To rule out parasomnias you need to undergo Polysomnyography and sleep analysis. She needs to take out time for further evaluation. Sleep with light on. Short term benzodiazepine against prescription will help. I suggest her to consult physician or sleep specialist. Take care and regards.