I'm going to tell my late brother's ex wife to fuck off
Why do you want his ex-wife to fuck off?
I think she's the reason why we're fighting now
Even if you think they are too blame for something, you shouldn't tell people to fuck off. It is rude and you will look aggressive.
I don't care what you say I'm going to yell at her.
It sounds like you should just ignore this person entirely if you hate her this much.