Seeing as the drooling seems have to started suddenly it would be worth taking her back to the vet.

I'm no expert but have heard that this could be related to tooth trouble or other things not quite right in the mouth.

Or could she have eaten something she shouldn't such as a piece of string, dental floss etc?

Sorry to be painting the devil on the wall here - hope I'm way off but do give the vet a call about this