She tried to kill her, yet everyone is probably gonna keep blaming the wrong person. It's how a lot of these stories go sadly.
This is why violence IS the answer. Just claim self defense and take her out, no matter what anyone tries saying to the contrary, she attacked first, so anything she gets in retaliation should be acceptable.
Brother is a pos too. He'll probably simp out or just do nothing and then it'll just be unreasonable actions to interrupt later as if he's just executing his own "justice" while blind to what's really going on.