The latter.... She decided to go on slicks where everyone else decided to go out on intermediate rains, or full rains.
If you look at the inset box in the bottom right, you can see how much she is fighting the car to keep the nose pointing forward.
Amazing driving from her
Her car was quicker than some of the slower class cars at the beginning, yes. But by the time she reaches the Nordschleife part on the 1st lap (basically at 2:12), she's among same 911 RSR class cars, and she just tears them up from there