You shouldn't be afraid to tell her that you like her. I mean, I have friends who are bisexual and I keep them as friends and so do others in our little group.
I'm telling you this because I'm sort of a tomboy too. Seriously though, you shouldn't be afraid to tell your friend. If they stick by you, then they are a real friend. If they don't, just get over it and find someone else you like.
Don't worry about people making fun of you. All of us are one in a million. Don't be afraid to show your true colors to the world even if they reject it.