What should I get my girlfriend for Christmas? She loves dance, cats, clothes, makeup, etc... She tells me she doesn't want anything, so its hard to even get some sort of an idea of what to get her. I want to get her something meaningful without saying we're engaged... I want to get something romantic, meaningful, and something that says I love you. Any ideas?

A gift from the heart is your best bet. You know her better than you can describe to anyone here, so our advice would only be secondary to the knowledge that you have of her.
I personally would go with a theme that she likes... cats obviously. I'd go with a figurine of a cat, possibly her favorite breed, maybe on a stand, and have a plaque on it, and have something engraved on it.
Again, you know her better than I ever could, so it should be something that comes from your heart.