Just be honest and let her know you feel more comfortable in girls clothing. You do have to be fair about this and understand that if you go out of the house this way, unfortunately, it will not be taken well by outsiders. There are alot of unisex clothing, not so much girls clothing. In other cultures, men wear wear dresses and skirts and not just for rituals and musical purposes. I saw a guy wear a cool pair of clogs the other day with a past the knee skirt, you could tell he was european, I thought it was cool and thought he was cool for making the statement, Im going to wear what I like. There is too much emphasis put on machoism in this country and daring to be different can make you an target. Just be careful