Hello and thank you for asking your question. My name isXXXXX will try to help.
So the most likely cause is allergies. I do not think it is due to boredom of lack of appropriate things to chew on.
Hopefully your vet, or the dermatologist, has done a blood test to see what she is allergic to. Environmental allergies are called "atopy." The allergens go through the skin and cause an allergic reaction. The blood test will tell you what she is allergic to in the environment. Then, she could receive allergy shots to desensitize her to the allergens. The allergy shots are 50-75% effective in pets.
She could also have food allergies. The most common food allergens are beef, chicken, lamb, wheat, and corn. So try to find a food that avoids those. I feed mine "wellness limited ingredient" or "proplan sensitive skin." The only true way to diagnose her with allergies is to put her on a completely hypo-allergenic diet for 6 weeks. But again, you have to get the completely hypo-allergenic diet from a vet.
There are a number of things you can do, at home to try and help.
If her feet are incredibly itchy, she could have sarcoptic mange. It commonly affects the ears, and feet, and causes intense itching. The vet could do a skin scrape to see if she has the mange/mites. It can be treated with an ivermectin type medication.
Every time she comes in from outside, wash her feet. This is to remove the allergens so they do not enter the skin. Try to do the shampoo, and water, once a day. The other times you can use baby wipes. Make sure you get between her paw pads. Leaving the allergens (grass is a common one) on the feet will cause an allergic reaction.
This is a good anti fungal and antibacterial shampoo.
You can also give her human antihistamines. Try benadryl to start. The dose is 1 mg per pound of body weight every 12 hours. For example, a 50 pound dog would get 50 mg of benadryl every 12 hours. If that does not work, you can try one 10mg tablet of zyrtec once a day. You can try other antihistamines as well. You will need to give it every day to prevent problems. Do not just give it when she is having a reaction.
Giving omega-3 fatty acid supplements can help as well. They sell "3-V caps, and liquid" online and at pet stores. Or you can try fish oil from the health food store. Start with 1/2 teaspoon, twice a day, on her food. Then you can gradually go up to 1 teaspoon twice a day.
You may want to put a plastic cone, on her head, to prevent the licking. You can buy a plastic elizabethan cone collar at a larger pet store.
It is probably going to be a lifelong problem.
If it is not allergy related, then it is due to anxiety. In that case, putting her on an anti-anxiety medication will help. You would have to get the anti-anxiety medication from a vet.
I think the next step, is a recheck to the dermatologist. You, or the vet, should be able to find a medication combination that stops the food licking.
I hope this helps.
If you have additional questions, please click "reply." Thank you