It may seem incredibly stupid, but whilst polyjuiced as Jory, Ari wanted to do all the things she couldn't do as a girl, which included entering the boy's bathroom. She still had a shock seeing her reflection in the mirror, looking as a boy. But being in the boy's bathroom actually gave her satisfaction for being able to break school rules, even though it was a minor one. For a first year, this had been a challenge, all right. Good thing she didn't need to pee, though, because that would have been plain weird.