When you' re talking about the first date, you mean the tennis match, right?
I think I understand what you mean, but I don't take it that badly. One shower was broken, so they had to take a shower together. Since Jill has a completely different environment than the MC and because she likes him, she trusts him of course when he says he's not peeking. She generally seems to be a very positive person.
What happened in the shower wasn't on purpose. Afterward, they just kissed, which in her opinion is quite normal for a first date.