Hair loss on a boxer.

I've had Kizzie for two years. She's a vibrant and playful dog. Recently, I've noticed that her hair is thinning on her sides and in some spots there are scabs, sores. She does not scratch excessively, but I noticed when I bathed her recently the affected areas dried quickly and turned white. She is warm brown in color and I can see her skin in the affected areas. It looks slightly red and irritated. Although the thinning is localized to the sides of her body. Her overall hair is looking thin all over. Her hair is fine in texture and is short. I've already had her thyroid checked and test results came back normal. A local vet recommended putting her on Benadryl. She has also not been spayed yet, which the vet said could impact her hormone levels and thus prompt hair loss. I wanted a second opinion. Kizzie is a house dog and not around many other animals. I'm looking for recommendations on how to best treat her condition and prevent the condition from spreading.

Thank you so much for any advice you can provide.

Sincerely,

Tajuana and Kizzie