I keep asking if she wants to go and she gives a different reason every time all of which (besides only wanting to go to senior prom) are things I can resolve such as paying class dues. I keep telling her and asking about going and me wanting to go with her and only asked about going with a friend (crush a year ago but just a friend now) and her friends. So ya...
Have you asked why outside the context of trying to get her to go? It's probably best to assume she's made up her mind, and figure out how to work around that. That said,
(crush a year ago but just a friend now)
is hella dangerous, especially if your girlfriend knows it. From her perspective, that's essentially saying, "If you won't do what I want, I'll replace you."
Now, the problem is that she's almost certainly not looking at it from
your perspective, either. It sounds to me like you both rate yourselves on what you think and feel, and the other on how they make you feel. It's not a healthy way to take a relationship, and you know why - all that abusive behavior you're dealing with is because she doesn't empathize with you in the same way she empathizes with herself. While this mutual hedonism persists, it's going to create a spiral of passive-aggression and doubt.
I'm not entirely sure how to resolve it. I know you need to take the first steps, but that's not guaranteed to work. If she continues to demonstrate an unwillingness to appreciate your perspective (that is, when you're not presenting it in order to convince her of anything), then you do have to be willing to consider that the relationship may not be worthwhile. If you're the only one trying, she'd just be taking advantage of you; same as if it went the other way 'round.
So, I guess, explain what you're feeling with trying to get her to do anything; don't try to get her to go to prom, don't get her to try to change her behavior, and for god's sake don't try to make her feel bad because you feel bad. If that helps, great. If it doesn't, then you'll have to set boundaries for what you can handle, be willing to disengage when she crosses them, and consider how that's going to affect the relationship. If she continues trying to manipulate you, and that stress isn't worth it, you may need to end it.