I've been wondering why (presumably) Riri sent the perfume to Fujiyama in the first place. After all, it's not like she couldn't just go over to her house and ask to hang out, right? I mean, she dropped off the package there.
I can only come up with three explanations:
1) Fujiyama's apartment is dangerous territory for a dark magical girl, considering that her target is flanked by the most badass magical girl ever and a very temperamental magical girl, so being there physically for very long is not a good idea
2) She wanted to guarantee time alone with Fujiyama so there would be no interruptions (unlike last time)
3) Her ability to corrupt and alter things works better in situations of isolation
I strongly suspect it's #2 with #1 being also true, but kind of an afterthought. I'm the least confident in #3 being the case, let alone being true at all.