It does sound like allergies or very dry skin. With food allergies you will also see a rash around the belly area, seasonal allergies will have the dog scratching and rubbing the muzzle along the ground, furniture,or anything that is rough. Our vet can do allergy tests to determine the cause if you choose that route. Sometimes the allergies stop when the season ends.
Benadryl can be given to help with the itch and I will direct you to a site on this that will have a dosing chart. http://www.petplace.com/drug-library/diphenhydramine-benadryl/page1.aspx
I would also start the dog on daily omega fatty acids to help strengthen the skin and coat. Fish oil or derm caps are good for this , but there are many products on the market for dogs with this. http://www.petplace.com/drug-library/fatty-acids-omega-derm-caps/page1.aspx
If the dog has worms this would not affect the scratching and muzzle rubbing. Generally you would see scooting the anus along the ground with worms. However the worms may be making her immune system weak. I would have th worms taken care of if you haven't already. Go through your vet for this as most over the counter stuff does not work as well.
Here is a great site on worms. It will have pictures and tell you what the worm is capable of doing to the dog.
As for seasonal allergies if benadryl isn't working then the vet can give a shot to help with the itch.