If it was full lip synching then how could she flub? When she didn't get the line, there was silence. If she had been totally lip synching the line would've still played. She sings/raps OVER the tracks, sometimes does it more independent sometimes has the tracks higher.

Nicki sings & raps over the track. You could tell when she stopped (such as the small flub in the 2nd verse of Bed of Lies, or during one line in the 2nd verse of All Things Go where the track played while she wasn't rapping). It's not exactly lip-synching.