Freedom - 6:20 pm on Aug 11, 2011 (gmt 0)
I don't think that's necessarily indicative that something is wrong at FB. Six years at a top post at any company is a long time and perhaps it was seen that it was time to get someone else in there or that dept. would stagnate.
Or, maybe she wanted to get out of her brothers shadow, and do her "own thing." Make a name for herself instead of just being "Mark Zuckerberg's" brother.