This kind of stuff bugs me. We'll never know the exact situation, but I have a REALLY hard time believing she was unaware of the situation.
Also, while I can appreciate a person's privacy during recovery, I see nothing wrong with the band stating her illness, and the severity of it. Like she said, she's on chemo - this is not a small matter. She's HALF of the band, and fans need to understand she'd be there if she could.
Final thought: I don't like when musicians publicly speak out against their bands. If anyone in a regular job did this, they would be fired immediately. If it tears her up so much, then quit; if she feels left out, or taken advantage of, quit. Otherwise, keep band drama internal.
She kind of isnt in the band at all anymore. Jesus dude she has a serious fucking illness. Have some sense.