I'm going to get my friend fired from her retail job at Christmas.
Why would you want someone fired right at Christmas?
She never thanks me for lending her money, even though I always do.
I get being annoyed, but the answer is not to get her fired. That will just hurt her and whoever may depend on her. You should just stop seeing her instead.
I want her to be polite to me for a change.
It's understandable to want a friend to treat you better, but having them fired will only cause more harm than good. You could seriously alter her whole future by having this on her resume.