Really? Beautiful is perverted? Well say to her that you find her very appealing, surely she won't have much to disagree there? Some women just don't know how to take complements, what would happen if you just said "i can't get over how sexy you are" would she just call you rude? X
She is wierd. She probably has some bad experience. Try some subtle way to find out how she calls herself when she feel really good. Or how she calls her female friends when they are beautiful at that moment. Use that word and sexy tone of voice! I guess she has pretty bad experience with words sexy and beautiful. But there are surely some words she uses and those are words that has most positive meaning for her.