The first thing to do is to review her medications. The quivering is sometimes a reaction to certain medications and is part of a syndrome called tardive dyskinesia.
So what medications/supplements typically cause this? My lower lip quivers when I play sax. It sounds like I'm nervous, but I'm not. It feels like the lip is weak, but I've been playing way too long for that to be the case. Thank you.
Librium is the primary cause of lip quivering, but other psychiatric meds also are often responsible. Of course there may be other reasons not related to medications.