What Causes Severe Weakness And Tremors In The Right Hand?

My 19 yo daughter has been having episodes of weakness in her R hand. She will be holding an object and then just drop it. She also has episodes where her hand will jerk and she will drop something or her arm will jerk and lose control and drop it. She has dropped several bottles in the last few weeks while in a store breaking the bottles. This has been getting worse. I had a OT check her for carpal tunnel initially which was negative. She has gotten weaker all over which we attributed to her loosing about 25 pounds as she was running and not doing any strengthening. Looking at her whole picture now I am afraid there is more going on. She is paler, weaker, tired and having these loses of control of her hand/arm. She doesn t feel her hand get weak she just will loose the strength. She went to hand an object to a customer and her hand jerked and went weak and she ended up throwing the object across the counter at the customer due to her loss of control. I am setting uppity her primary physician but would like some input and more questions to ask. My fear goes to all the bad diseases like MS!