Hey mate, I'm new here too, I've got a few options for you. Don't worry, rhymes aren't usually my strong suit.
#1, throw a smoke bomb on the ground, vanish mysteriously
#2, stand on the nearest table and preach about CHANGE
#3, get her details before the conversation dies and it seems strange. "hey look, I guess your pretty normal after all, do you know how to work a phone? Stick your details in here."
#4, end the conversation while it's still going well. "I've got to go right now, but before I do, put your details in here *present phone preferably without peanut butter on it. Oh hey, if a guy with an eye patch and a western hat asks if you've seen me, say no."
By using any of these routines, bar #2 you're taking control, and making her chase you. Really, she can't refuse what you've said, unless you're a complete dolt. You leave while the conversation is on a high (DHV in itself), as soon as that feeling for her is gone, she's going to want it back.
Cheers.