I agree with that it was only another uncharacteristically insensitive act. Rin trusted Hanayo the whole time. She only voiced her confusion and reacted to the pain, but didn't try to stop whatever Hanayo was doing. It not being rape doesn't mean anyone should take it as an example to be followed, though.
Yeah, this is kind of a morally grey area, uncharacteristic behavior aside. Passive compliance doesn't exactly equate to enthusiastic consent. But I think it's also rather realistic in that inexperience can and does often result in such "blunders".
But then again, I'm applying real world logic to cute cartoon girls that somehow both live in a world where men apparently don't exist, yet somehow also seem to have virtually no idea about How 2 Lewd despite being like 16--at least until someone "flips their switch" and then they suddenly become Super Knowledgeable Super Lesbians, Woo!, so I digress. lol