Hi, welcome to the forum, it seems to be a manifestation of type of sleep disorder like parasomnias, wherein the certain events occur without the knowledge of the person.
Few of the individuals are known to suffer from parasomnias esp. when they are on non-benzodiazepine sedaives, 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 she needs to undergo Polysomnyography and sleep analysis. she needs to take out time for further evaluation. Ask her to sleep with light on. Short term benzodiazepine against prescription will help her. I suggest you to consult her to a physician or sleep specialist. Take care and regards.