Could be an allergy or a hot spot. Bathe the area with selson blue and make sure there are no fleas. If it keeps up, see the vet.

If you are in an area where parvo is prevelant, those are signs.  I would seek a vet as soon as you can.  They will dehydrate quickly and that is why she is drinking, but quick vet attention is the only help for parvo, esp if she is under 6 months.