A. It could be a sign of a tremor, which if she is otherwise healthy and growing and developing normally, is not necessarily a sign of any kind of serious disorder.
In fact, there is a condition called familial tremor, in which involuntary shaking runs in the family. Children can also have an essential tremor or shakes for which the cause is unknown.
Having a tremor can also be a side effect of some medications and certain metabolic disorders, like hyperthyroidism and hypoglycemia. In general, you would usually expect it to happen more often if a specific medical problems was causing her hands to shake.
See our symptom checker guide to tremors for more information.
A visit to your Pediatrician would be a good idea to get this further evaluated. Most importantly, that will help you figure out if what she is doing is really even a tremor. And then a physical examination, including a complete neurological exam, can help to figure out what is causing her hands to shake.
A Pediatric Neurologist can also be helpful if she is really having tremors, although children with essential and familial tremors often don't need any kind of treatment. They can be treated with beta blockers if they do cause a problem later on, like if it causes difficult writing because her hands shake so much.