I agree with Pitbullo but it would help if you mentioned what lens you are most comfortable shooting with and what your goals are with the pictures. Are you trying to achieve portraits that isolate your girlfriend, landscapes with her in the foreground, mostly indoor, outdoor, day, night, etc. Since it sounds like you will want to do it all, I would get wide lens like the 17-40 or 16-35 and a longer lens like the 24-105. Or you could even get a Tamron 28-300 VC ultrazoom for walkaround. If you want nice portraits, get a 28/1.8 or 50/1.4. Both would double as nice low light primes. It all really depends on your style of shooting. And don't forget a flash for fill. Good luck and hope you have a good time!