Since it's your GF, if you have the $$$ to fix her car after it is tuned... then sure do it otherwise I wouldn't touch it cause if something goes wrong and you can't fix it she will leave you for someone that can or has the $$$ to fix it.
I'm in a different situation since I had some GTI parts left over after selling my GTI including a K04.
So I told my wife that I was just getting her VW CC serviced and a tune up
Instead I
-had the K04 installed with APR software
-installed APR intercooler
-installed B&B downpipe
-installed VF DogBone instert
-installed thicker rear sway bar
-installed Stoptech pads
She never realised all the changes I did on the car after she drove it
-if anything since the Ko4 characteristics where different from the oe K03 combined with the stock DSG... the car felt slower to her at part throttle
- so I said just push the gas all the way down... and she LOVES it!!!
Since then I added a Gold Coast Body kit along with the Neuspeed RSE14 wheels from my GTI, Unitronic DSG software, and most importantly a hardwired radar detector since she has gotten pulled over at least once a month since doing the above mods (but has gotten out of every ticket)