if it's a birthday present consider a gift certificate to a LBS you've checked out and like (one that communicates well, has a good reputation for service, etc).

Wrap the gift certificate and present it to her on her BD. Or ....

Take her out for dinner to an eatery near a LBS. Casually stroll by the shop on the way or after "oh, let's just look in" and casually mention "Happy birthday darling, look around and when you're ready I will buy you the bike you want." Or ....

Get her a bike jersey (hint, from TE. See link above and to the left to shop). Wrap it up.
"But honey, I don't have a bike. "
"Look in the jersey pocket" And put the bike shop GC there.

Chicks dig this kinda thing YMMV oh, and introduce her to this forum.