As long as you are clean and of clean appearance I see no problem. I assume you are right on top of your other hygene requirements.

Is there a reason you mother thinks otherwise?

Regardless, your appearance is your choice and not hers. If after a good discussion about this where you vocalize your own good reasons she keeps interfering and making demands it is time to make demands of your own. If she won't respect this I think what is called for is a withdrawal and pulling back from her.