Thanks, Lana, for sharing and asking. It is impossible and unethical for me to attempt making a diagnosis of your friend's condition. Sleep deprivation and certain antidepressants can exacerbate hypnic jerks. Typically, the treatment approaches are to avoid stimulants (nicotine, caffeine) prior to bedtime. But she did that already. Another possible cause is low magnesium. I assume her doctor has investigated that already?

A low-dose anxiolytic med (e.g. clonazepam) may be worth discussing with her doctor. In her case, my suggested midnight exercise may not be suitable.