Is your girl on any medications?
How is her appetite?
Is she walking pretty normally for her?
Any weight loss?
The increased thirst is more of a concern than is the itching right now. I do not how uncomfortable being itchy can be so I will suggest you try a dose of benedryl to see if this creates any improvements. The dosage for dogs is 1mg per pound. If you see no improvement after one dose then don't continue it.
As for the increase in thirst this can indicate a number of condition or cumulative conditions may be present. These include kidney disease, liver disease, diabetes, urinary tract infection, hypothyroidism, and even Cushing's disease. Since your dog has two major symptoms of excessive thirst and skin issues I am leaning more toward a thryoid condition as well as possibly Cushing's disease.
It would be in her best interest to visit the vet this week for bloodwork and a urinalysis to rule out the mentioned ailments above.