The "HEY!" is a bit surprising, and "Do you have email"
is non-threatening. In fact, I'm technically asking her if
she HAS email, not if she'll GIVE IT TO ME.

If she says "yes," I take out a pen and paper and say
"Great, write it down for me" and I have her write it down.
(This is great, as I just treat the 'yes' that they
give me as a yes to get it from them as well. And they've
almost ALL gone along with it so far) Then AS SHE'S IN THE
MIDDLE OF WRITING, I say "Write your number down there too."