My wife is thinking about it too, but she's unsure of design and placement.
So first start out with the temporary tat's and see where she wants it. I recently got gf a few (they come in packages) and she's put them on but only wears it around the house. This is a slow procedure. I'm trying to get her to wear it when we go out in public. So far, she's put them on her chest and ankle. Putting one on her butt is kind of a waste if you ask me. I don't want her to get a real one because I dislike any permanent tattoo's on women.