Alrighty so first you kind of want to clue her on. Trust me girls easily pick up on if you like them or not. Or at least I do! Compliment her to tell her how beautiful she is. Trust me this should work! Then just tell her! Say that you dont want to make things awkward but you have feelings for her. if this ruins your relationship she's not worth it!
if she says no then just day to her oh well at least i tried!