pick e-mail and phone

"Hey, nice talking to you, but I have to get
back to my friends (or what I was doing, etc.)."

Then, just as you're turning away, say:

"Hey... Do you have email?"

When she says "Yes", just take out a pen and
paper and give it to her, expecting her to write
it down. When she does, say, "Nice meeting you,
I'll chat with you again when I have some more
time..." and walk away.