Poor Tasha!

It's too bad that the food switch and the leaf incedent all seemed to happen at the same time. I would place my bets on the leaves though. They say 85% of dog allergies are environmental. I don't know if I'd keep her on the prednione -- but I am not a fan of prednisone.

I'd put her back on her regular food, and see what you can do about cleaning up the leaves in your yard -- and maybe just limit backyard visits and take her pee in the front yard instead? Diphenhydramine is a component of heroin and can cause similar symptoms as the drug -- mostly it causes drowsiness though. It's least likely to cause anything in shampoo form, but to keep those chances low make sure she doesn't lick it.

We're treating a dog at work (with a terrible staff infection all over) by bathing her in vinegar, force drying her, and first spraying her with colloidal silver before rubbing tea tree oil and oil of oregano into her skin. It's working very well. She is also taking the oil of oregano orally, and the silver is being added to her water. It might be worth a try. My rat is itching himself raw (he has bald patches and scabs all over his body -- I believe the mold in my house is the culprit), and since I started bathing him with my own mixture of shampoos (oatmeal, peppermint, mango, papaya, coconut, lavendar, aloe, comfrey, callendula, etc) every day, and adding colloidal silver to his water, he has really improved.

Good luck with Tasha, keep us updated on her improvement.