My mom cussed me out and says my head is full of shit. Getting tired of her involving me into her manipulation. What can I do/say?

First off, I’m 17. My mom let my stepdad borrow $100 but she told him it was my bf’s money because otherwise he’d take his time to pay back. Today, she told me to go pick up food that she ordered for all of us but she wanted me to ask my stepdad for money (to supposedly pay for the food) & tell my bf to pay it, then give her the money my stepdad gave me to supposedly pay for the food. She’s in debt with the phone bill and a bunch of jewelry that she has pawned. I didn’t ask my stepdad for the money because I only heard to ask him for the $100 that are hers. She called me mad asf because I didn’t ask him for money to “pay the food.” She was saying my head is full of shit and I get stupider as each day goes by. Im honestly so tired of her verbal abuse. Im tired of her manipulative ways with everyone. She’s always asking my bf for money. She works. I can’t work because I have to babysit my brother since she said she “won’t pay $20 for someone to look after him if I’m there and able to do so for free.”