We have allergies and use Temeril P (very low dose)for the itching and it seems to help. You may also try changing to a fish and potato or venison and rice food. Most vets recommend lamb and rice or beet pulp free, but most dogs are allergic to the meat so it's usually not the wheat or beet pulp. Ours is allergic to beef, pork, lamb, chicken and turkey. And numerous grasses and plants. Also read the label completely; some list animal fat as an ingredient. What kind of animal fat.
Where are the red spots? Are you sure they are from allergies? Mostly on her feet or all over?
Have you moved recently or planted anything new?
Has she been tested for allergies?
What breed?