An art gallery, because everyone is stupid.
She hasn't. The twist is that it ended up in the infants section because of how much it looked like something from an elementary schooler. Her dad then proceeds to punch his son for showing up and then Nitta for encouraging her.
Huh, i thought it was pretty clear since the chapters whole punchline was that he was hitting on his sister. Though with this board, and probably Japan in general, the thought that hitting on your sister be a bad thing was completely foreign.