She didn't wake up until midday. The amount of magical energy that was required to not only create the initial containment field, but then to conjure up Fiendfyre she could hold in her hand even for a few moments was astronomical. There was a very valid reason why so few ever wanted to attempt such a spell. Also, the fact that Vincent Crabbe wasn't able to control it when he was a foolish teenager proved that not everyone understood that energy had to come from somewhere.