First off, Grafton Street. Second, Temple Bar. Or vice versa. The shopping on Grafton Street and it's environs is really fun. You can wander into Stephen's Green (very Dublin), or north towards Trinity College, where you can combine a trip to the Book of Kells (a must-see) with hanging out and watching the college kids, maybe even find something on campus to do with her while there.

Wandering from Temple Bar across the Ha'penny Bridge, take her into the Winding Stair Bookshop upstairs (a great, inexpensive place to have lunch or tea). On Grafton St, definitely do Bewley's. Any of them really, but Grafton St is best. Tons of Dublin kids hang out at the McD's on Grafton St too, right across from Bewley's.

Take her to the street market off O'Connell Street behind the GPO during the day, but hang onto your purses/bags, as there are lots of pickpockets in the area.

Also, the huge record shop in the City Centre...what the hell's the name of it...she'll like that too.