I am thinking that I should refuse to pay for my roommates pizza.
Why do you not want to pay?
We have a year long disagreement.
It is wrong for someone to expect another person to pay for a pizza they ordered. You should talk to them and let them know it is not ok if you didn't order it together and make a plan.
It's not my fault I'm broke and I'm going to let out my anger by ruining her life.
Whether you have a conflict with your roommate or not, it is not fair for them to expect you to pay for their pizza. You are not responsible for feeding them, so they should expect that they will be paying for their own food.