Do this: But you have to do it without creeping her out. Try to come across like a normal decent human being she'd benefit from knowing. So go up to her and say with this intro-"I hope this don't sound too strange but..". be sure to start that way rather than just blurting your proposal out. Then say something like I've noticed you for a time now and well I was wondering and hoping that sometime we could go out for a coffee and sit and get to know each other a bit. You won't know until you ask and what harm can come. She'll likely say "oh that sounds nice and thank you for asking but I'm married or I have a steady boyfriend" Then you will be able to move on. Be sure you look nice. Don't wear jeans unless they're nice. Make sure your nails are clean and well trimmed. Make sure you smell nice or at least not badly. Always watch your behavior that you don't as they say creep her out. If you do you'll get nowhere with her.