Ok, I just don't understand...
First, Ririha wants to "completely rob that which Yuzumori hold dear". And lets agree that could made Yuzumori sad and cry, right? (chap.18.2)
Second, Ririha gets annoyed when Yuzumori dont become sad (chap.25)
And now, when Ririha sees Yuzumori crying she helps her?
WTF logic is that? First Ririha tries to upset Yuzumori, and finnaly when Yuzumori gets upset she helps her...
You could say that is because Yuzumori was getting "abused" by an older girl... But c'mon... It's not like the scene was a creepy old man trying to touch her special spot! (in that case I could believe that Ririha would help because that's fucked up) The scene was: a cool looking older girl scolding a child. Teens scold kids all the time... and kids cries all the time for stupid reasons... Ririha overeacted... Even Isuzu was like "what are you doing you crazy slut!?"
But yeah, I guess Ririha is lesbian for Yuzumori after all...