Hi Sir or Madam,
How old is she?
What breed is she?
Is there hair loss?
Is she on flea preventative?
If so, what kind?
Where on her head, face, etc is this scab?
Is she missing hair on the edges of the ear or around the eyes and muzzle?
Is she itched other areas?
I'm not saying this is from fleas, but you should have her on flea preventative. Even if she eliminates inside and never goes out EVER, fleas can jump on the humans and be brought into the house. They can travel in on visitiors who have pets, so being a totally inside dog does not ensure she doesn't have fleas. Once fleas are in a house, the eggs can get into the carpets and furniture as well. So I would get her on flea preventative to ensure fleas don't become an issue.
Itching can be from a variety of causes including fleas, allergies, mange mites, dry skin to name a few causes.
From your description of her having itchy ears and nibbling on her feet, this could indicate that she has allergies. Dogs with allergies will frequently have frequent ear infections. An allergic reaction is often the cause when a dog is excessively licking and/or chewing their paws. Thyroid problems can also cause paw problems as well. It's possible your dog has developed a secondary staph or yeast problem. If yeast you can try some miconazole cream on the paws and ears to see if it helps but it isn't a cure for underlying condition.
You can try baby socks to prevent your dog from licking them. You can also give your dog some Benadryl. The dosage is up to 2 mg per pound every 8-12 hours. Start with 1 mg per pound first and see if it doesn't help the situation and provide your dog with some relief.
Here is a site on dog allergies
However, mange can cause a dog to scratch and in the case of demodectic mange, it usually starts in the facial area and you see a progressive thinning of the hair as the mites multiply unchecked by the dog's immune system. These mites usually occur in dog under a year of age who have an immature immune system. It is diagnosed by a skin scrapping. You can read about mange here:
Here is a site that goes over itching in dogs.
For now, you should clean the scabbed area with antibacterial soap, disinfect with hydrogen peroxide and apply neosporin or triple antibiotic cream. This is more of a precaution since it is already scabbed, but the scab may come off and then this cleaning will help it heal faster.
Given that she is having a lot of scratching to the extend that she may have caused the scab herself and still is scratching her ears and chewing her paws, I'd go ahead and have her seen by your vet so a skin scraping can be done and she can be evaluated as to the underlying cause for her symptoms.
I hope this information is helpful to you.
Be sure and read the sites I gave you so you are familiar with these causes. It will help you discuss possible treatment methods with your vet.