One common misconception is that all censorship is done automatically based on keywords. While it's true that internet searches in particular, and visits to banned websites are greeted with a connection reset, the censorship of message boards is done by hordes of low-paid individual workers (the "50-cent party" [1]) that are local to each district. Your girlfriend's post (which was a one-word post, and an inflammatory one at that) was probably spotted by whichever worker(s) were responsible for monitoring that message board.

When such a post is removed, it's typically referred to by netizens as being "harmonized", a play on Hu Jintao's "Harmonious Society" slogan [2].

You should check out the archives of a site like chinasmack or chinahush[3], who have translated summaries of popular chinese message board topics and gives a good feel of the day-to-day life of a chinese netizen.

[1] http://en.wikipedia.org/wiki/50_Cent_Party

[2] http://en.wikipedia.org/wiki/Harmonious_Society

[3] http://chinasmack.com http://chinahush.com