I don't think you need to worry too much about her not understanding everything down to a T. I'm a native German speaker and when I met Mr Elle 11 years ago I was reluctant to see a Shakespeare play with him, being afraid I won't understand everything. I was fine... Once your gf is getting more and more exposed to those series she will definitely get it - maybe not the first time around. Believe it or not, Germans do have a sense of humour (I know we are not supposed to...) and it's quite a bit like the English one ( We DO get the major in Fawlty Towers and we Do laugh about the German episode - even though the spoken German there really sucks it it gets kind of 'over-quoted' by PDLM here ). Frankly speaking I'd hate subtitles. If your gf is a keen reader give her some Ben Elton, then follow up with Tom Sharpe (this is what Mr Elle did with me)