Ah, I also suspected her, but I wasn't sure. I could tell from Reimu's words though and I just inferred that she was the culprit.... She was on the top of my list while I tried solving things, but with such an explanation like the one given up top, it really makes me wonder about why the culprit had done the crime. Why did she want to kill her? Not exactly want though since Reimu mentioned stuff like that.
I read through that one messy whack of translated dialogue and was confused as fudge (cause of the amazing translation). But I never really do know though... Maybe I'm just being dumb right now, oblivious to the reality of the situation, or acting like a child but there are some things you can't know, I guess?