diwan3474,
It depends upon the cause. If is is due to trauma, then it will most likely just go away on its own, with a little time.
But, if it is not due to trauma, then the cause has to be determined, because the treatment has to be aimed at the underlying cause.
For example, if it is due to a bleeding disorder, then the bleeding disorder needs to be treated.
She should be seen by her pediatrician for a thorough evaluation.
Good luck.