Well she would agree with everyting she says. She would look at her boobs or her bum. Flick her hair and lick her lips. If she is really crushing on the girl she would try and stroke her and play with her hair.
1st of all, how do you know she doesnt like you? 2nd...dont just plain out say you like her...let her get to know you...its much easier for her to fall for you if you're funny and fun to be around....
I'm not sure it would be the same as telling someone of the opposite sex, because it's political, and you're changing someones perspective/ views, you don't know if the girl shares them same feeling,...
It's actually a lot easier than you think it is. If you put yourself in her shoes, wondering how she would feel being told that someone likes her, you might understand more that what you have to say...