Skin condition in older female boxer

Question
We have a female boxer who joined our family 6 years ago. The owner at the time claimed she was 10 years old, so I am not sure of her exact age, but she is up there.

About 5-6 weeks ago, she started getting bumps on her skin that did not seem to itch her. Within a few days, they spread and her skin was warm to the touch. We took her to the vet - which is very hard on her because it hurts her to get in/out of vehicles and walk around too much. She did not have a fever, but we were told that the warmth was due to inflammation from a skin infection.

We were given Cephalexin 100mg twice a day for 3 weeks. The vet gave us a medicated shampoo (BPO-3 Benzoyl Peroxide 3%)to bathe her with once per week for 4 weeks.

She is also on Rimadyl, 50mg twice per day and Tramadol, 25mg twice per day, for pain.

Her food is a combination of Diamond Lamb & Rice and Evo Red Meat.

From my online research, it looks as though she has Demodex. Whatever it is doesn't itch her until I touch it. It's apparently not contagious because nobody else in the house (humans and dogs) has it. Basically, it starts out as these bumps that eventually flake off with a small wad of hair attached to them. During baths, loads of these come off.

We finished the Cephalexin and the 4 prescribed baths and she still has the bumps - not as many, but they are still all over her sides/back, with a few on her face and chest. The skin has not been unusually warm or red. Whatever it is, it's obviously not gone.

Another vet visit is likely in the future, but I would like to hear some other input.

Answer
100mg of Cephalexin will not do very much for a dog the size of a boxer.  Based on the Rimadyl dose of 50mg, then she would need at least 500mg of Cephalexin twice daily.  

Demodex is very rare in a dog this age, but skin scrapings may show demodex mites.

If she had skin bumps that did not itch, that could be an allergic reaction to something.