Seems pretty obvious to me that she released it (and was holding it) before the BF hit it - Edit 1
Before modification by darius_sedai at 26/10/2010 04:40:35 AM
Graendal has trouble releasing the gateway, but I personally think she tied it off and was desperately trying to unravel it in time.
It's also possible that the balefire didn't 'reach' the weave by the time she released it i.e. the rest of the palace was being devoured by balefire and just before it hit her gateway she released it.
The way the text reads seems obvious that she had not tied off the weave and released is a sexing or two before the BF hit the weave.