My 11 year old Shih Tzu has developed a skin condition I need help with. Her skin is oily, crusty and she was itching all the time. I bought a medicated shampoo and some hydrocortisone spray which is making her feel better but I'm not sure if it will eliminate the problem. Does anyone have any idea what this is? Can I give her Benadryl? Anything else I can do to help her?