What Causes Tremors In Hands And Arms Despite Being Diagnosed With Rotator Cuff?

My Mother returned home from Rehab about 7-10 days ago. She is on oxygen, has problems with balance, ambulates with a rollator, has rotator cuff issues, DJD , CAD w/ bypass, DM,etc. In the past 2-4 days she has begun having noticeable tremors in her hands and arms. What are the possible causes?