Honestly... it sounds like if you DON'T tell her, you're going to be regretting it and asking yourself a lot of what-ifs.

So go ahead, ask her, tell her. You're right that it may very well make you feel worse.... but at least, in the long run... you'll know you tried. What else is there to lose, she's already turned you down once!

And yeah, emotions about people can change... but not usually through sheer force of will. It develops naturally. And.... well, I'm not sure that would be possible for you because you only want to be around her to have a relationship. If you were to be friends with her... it would be with that sole intention and you'll just grow bitter and angry if she never reciprocates.

You really have nothing left to lose by telling her as you've made it clear you don't want to be friends. So go for it!