Personally, I'm less concerned about her loving her brother and more concerned about her still loving someone whom she knows is/will be a psychopathic murderer (who is basically a yandere, too). Not the sanest of crushes.
I'm also understanding now how the situation at the start of chapter 1 came to be. Mai seemingly rejecting Makoto, together with his desire to kill Hase, make me feel like he's only a gentle nudge away from deciding a death game's a good idea.