Most Helpful Girl
Find a way to complement her : Either something she's done, her appearance or something about her personality that you admire :3 . But try to make it sound natural in conversation rather than out of nowhere so she's more flattered.
EG : If you really like her hair, bring up how you're considering a new hairstyle (or something) and then see what she says, and say "btw, your hair is cute/cool/pretty i think it really suits you" and smile :D
Good luck dude!
PS - Warning : Do not over compliment her as it might backfire or she'll get suspicious / feel awkward