This is even worse than the man with the band-aid! Kids don’t seem to be able to think about long-term consequences (or in this case, short-term pain) when they get a funny idea into their heads. Or maybe this was inflicted on her by a bigger sibling.
Either way, you’re the one who’s going to have to sort it out. Also, you’re the one she’s going to blame for it hurting, even though it was completely her idea. Because when children realize their mistakes a little too late, they can just blame a grown-up.