so sick of my mom

Every time I come up on some cash she wants some of it. She's asking me for $400 to get her car fixed because her boyfriend wrecked it. That has nothing to do with me. Why do you even let him drive KNOWING he never pays attention to the road bc he's always otp. I'm 18 & have a 2 month old to take care of by myself. Then when I tell her no she act like she's gonna "whoop me". She do this to all of her children. My brother is 15 & when he started working she tried taking his money too. Im tired of being bullied. It's never a "may I borrow" or "can I please have". It's always "when you get paid let me have this" or "when you get paid give me that" IM SICK OF THIS SHIT. But tbh im afraid of telling her no. She always wants to get physical bc she's my mom & think I'm not supposed to defend myself but I'm grown now. Im tired of slapped, punched, & getting my hair pulled. I don't want to fight her back but it's pissing me off to the point that I will.