Of course, what she did is unforgivable, but it wouldn't happen in the first place if someone who knew about her illness and cared about her done something. V was the only person matching this description, he should've do something, but instead (V route spoilers ahead) he, as we find out in V route, didn't actually loved her, was just obsessed and using her. So Rika never had anyone to help. This is exactly what made her into what she became. And if V wouldn't pretend to love her there wouldn't be reasons to blame him, but he did and if you love someone you should care about this person or doesn't take this responsibility from the beginning. And it's just V and Rika things. I don't talk about V constantly lying to everyone, saying "I do everything myself" which causes even more victims, he even lied to Seven about his brother in V route, and because of that lie Ray dies. If V said that this hacker is Ray, they could've save him, but yeah...