If it is bad enough that she feels self conscious and does not want to wear a bathing suit or shorts.. Please consider allowing her to shave.
I have always had dark hairy legs and I hated them..Some kids made comments and I so wish my mom would have let me start earlier.. She did not allow till I was in 6th grade and trying out for Cheerleader..
She is young enough in the beginning it will not grow back very fast, but do explain to her eventually it will..
And by the way, those rub off shaves do not work for dark hair.. It gives you kind on a wind burn feeling.. And they are not very thorough..