I would suggest a tanktop with no bra, and a skirt, with no panties. If she has pierced nipples, they will definitely show, which, even as I am a girl, I find a huge turn on... With the skirt, she can "sit" on you for a quicky, or just bend over. Also will make for some fun humiliation. The top can be heavier to not reveal as much, but that would be the masters call.