How do you show her your lesbian and like her if she's straight?

Well, why not imply that you are a lesbian. Then if you get so fed up because she can't figure it out then come clean and tell her. You could also let's say for example you like a blond blue eyed girl. Then you could say stuff like "blue eyes are sexy" or "blond hair is gorgeous".

In short you have two choices. One is to just tell her and the other is to be sneaky and imply it.