First, sarcastically praise her for doing exactly what she was supposed to do as a parent, then I'd be blunt and tell her to **** off. That's the problem with some parents, they think they're owed something for being a parent, they think they can get away with whatever they want because they provided for their kid(s). Newsflash, that's your ******* job and your kids don't owe you for it. It was your mother that accepted parental responsibility after she decided to have sex and reproduce, and accepting parental responsibility comes with financially providing for your child. That is the law, if a parent doesn't do this, they can get fined, get their kids taken away, or jailed. It would be like demanding reimbursement for obeying road rules when choosing to drive, congratulations you did what was expected of you, you want a medal? You did not choose to be born, you did not choose to be a child. However, she chose to give birth to you, she chose to raise you, and you do not need to pay someone back because of the choices THEY made and took responsibility for.

I hate it when parents do this. You didn't ask to be born, they chose to have you, or at least keep you, and if they did that without knowing the cost of raising a child, that's their own stupid fault. Don't give her a penny OP!