I am all for diagnosing ADHD if it becomes a barrier to learning and life. But at age 3, she is still developing and growing. I agree with the others, anything can happen. Keep in mind that younger kids are very hard to evaluate - IQ is developing in fits and spurts and they are supposed to be active and less focused.

Once she hits school, if there are major issues, then you may want to pursue your concerns. But for now, enjoy her exuberance!