If I don't want to see a movie I just tell her and she says ok and finds one of her gal friends to go with her. If she doesn't want to see something I want to see I download it or see it with somebody else. No arguments, no excuses, no deals, no negotiations. However, if she really wanted to see something with me that I had no interest in, I'd go because I know at some point roles will be reversed and she would say yes.
I'm guessing you can't just tell her you don't want to go without any blowback. My thought is you should get in touch with some of her friends and find a time for one or several of her friends to get together and see the movie. Then once you have it all planned out, tell your gal you would rather spend time doing something interactive with her (e.g. dinner) than see a movie you don't want to see but that so and so wants to see it with her. It's going to be hard for her to be mad at you for wanting to spend time with her and going out of your way to make plans for her to see it. Or you could just suck it up and see it with her.