LOL.......Seriously........read the last two pages of that chapter again and ask yourself if she really was trying. She just freaking knocked out one of them and caught the punch of the one who sent a guy flying.ヾ(❀╹◡╹)ノ~
Hell no......she wasn't trying. I think, she in her one twisted way want to break and at the same time love the camera dude. Σ(  ̄□ ̄||)
Well, I was just trying to give a reason as to why she was there. They're trying to essentially establish her as useless without him, and she's only so worked up once again after Machiya ordered her to do so. And maybe she didn't try to specifically save the sister, but she did try to fight those guys without him. But it's not impossible that she didn't let Kana die on purpose.
I'm impressed that he doesn't hate mashiro for not saving his sister - I'm glad their bond is pretty damn strong!