I'm gonna go ahead and assume that you're of high school age and therefore you live with your family.
First of all, I'd advise seriously against coming out. Personally, I think it's best for you guys to keep it on the DL. I know, it sucks real hard that there are people that are all "people are gay...***." but, it is true. If you really, really don't want to though, and you really want to come out, then you're going to have to do it slowly. Test the water, maybe find out why specifically she hates gays so much and maybe change her mind before telling her anyway.
Good luck, my friend.
(http://www.thefurryforum.com/forums/Themes/WZSkin/images/warnwarn.gif) Foul Language.