This is worth asking your vet about. It may be just a habit that she has developed, but it is also pretty common for the hair folicles of the whiskers to become infected and treatment may be needed. It may also be worth checking the inside of her mouth just after she has eaten as it may be that food is sticking to the roof of her mouth and she is trying to dislodge it.
My Retriever is very slobbery at feeding time and rubs his mouth on his front paws to make sure he gets every scrap of food that might be stuck there!