Is she on any medications? Is she Diabetic? Hypoglycemia which is a sudden drop in your blood sugar can also make you shakey. Or there may be issues with tremors. Consulting a physician is a very good idea.
This happens to me too. Does she have any medical problems? I have ashtma and arthritis and it might be a possibility if she has it to that might be why. If not, she might just be stressed out or nervous.