OMG, where should I start?
Culture and entertainment:
There are quite some events plus two operas and countless theaters, clubs,
museums, galleries and the like.
So for a starter, a guide might help to sort all this out:
http://www.visitberlin.de/english/suchen-buchen/e_sb_veranstaltungen_kultur.php
http://www.berlin.de/international/index.en.php
If your girlfriend is a flashaholic as well, maybe a "Berliner Unterwelten" Tour
(Berlin Underworld Tours) could be of interest:
http://berliner-unterwelten.de/guided-tours.3.1.html
Sightseeing:
City west and city east (downtown):
My usual tour that leads to almost all sights of downtown would be this:
Start at Kurfürstendamm , go to "Bahnhof Zoo"
(zoo station and yes, one of our zoos is right there) and from there
through the Tiergarten (sort of a central park) to the Brandenburger Tor.
Then follow the main street " Unter den Linden" to Alexanderplatz.
Take a guidebook to pick all the sights and places you want to see along this route.
(I think one can't do them all in two days)
If the weather is fine this will be a nice, minimum 3 hour walk, or for a shortcut
and if she don't needs a guided tour, go to "Bahnhof Zoo" and take the Bus #100,
as this one follows almost the mentioned route to Alexanderplatz.
Some other districts:
Kreuzberg:
Lots of pubs, restaurants and night live.
Points of interest:
"Potsdamer Platz", a newly build place with shoping mall, cinema, casino.
Nearby are the philharmonic concert hall, national gallery, state library.
The above mentioned "Museum für Verkehr und Technik" (museum of traffic and technology)
The area around subway station "Schlesisches Tor".
There's nothing of general interest to see, but I like the atmosphere of this place.
Prenzlauer Berg:
The new eastern night live and "in" district, especially around the "Kollwitzplatz".
The "Karl Marx Allee" nearby has a very unique architecture:
http://en.wikipedia.org/wiki/Karl-Marx-Allee.
If she's into castles, there's "Schloß Charlottenburg" and Sanssouci in Potsdam near Berlin.
For shopping shoes and these other women things, the malls at "Friedrichstraße"
might be a good place where all these designer brands are offered in fashionable
shops.
Of course I just could scratch the surface here, so if you need more detailed information,
feel free to ask.
Hope this helps somehow.
Thomas