Be honest with her.
Walk up to her and say "I can't get over how you look. I want to get to know you. Lets go get coffee or something.."
Practice your approach, recite what you want to say until no distraction can make you forget the words. Be calm and confident, smile, make eye-contact. If she says yes smile and give her your phone number. If she says no, smile and tell her you understand and leave it alone.