Maybe I am alone in this but I think if you genuinely want to practice drawing the human form go to life-drawing classes, that is purely non sexual. I think by asking this girl to pose for you (and I assume you wish for her to pose naked for you) sounds quite sly and creepy as your real intent is masked behind the smokescreen of a more innocent request to her to pose as your muse.

If that is the case, I find that quite unsettling.