She cleans up after herself and everyone else. Even though she pays rent, OP said her mom still treats her like a child and expects her to follow all of her rules.
She is considering moving with her girlfriend. If she moves, her mom will lose child support, and since the apartment is a three-bedroom, she could lose that, too.
"Your mother can downsize and you’re an adult that should be out experiencing life, if you’re able to afford it. You are not responsible for housing your mother and sister.”