I suspect your dog has allergies especially since she has had past episodes of skin issues. These can occur at any point in a dogs life. An allergy is the body's response to foreign proteins. Your dog could have inhalant allergies, contact allergies, flea allergies, food allergies, or a bacterial hypersensitivity. She could have one or a multiple of allergens. They can be seasonal or year round. You mention that this condition is chronic. Other symptoms are chronic ear infections, itchy skin, and recurrent hotspots.
Anti-inflammatories like prednisone and antihistamines should help to improve the itch and allergic response. If one antihistamine doesn't work then you try another. Benedryl doesn't always help all dogs and it must be given regularly and long term to provide good results. The recommended dosage of benedryl is 1mg per pound up to three times daily. If you have not tried hydroxyzine or chlorpheneramine then I would recommend giving them a whirl. These are great if they work, but if not you can try. Clemastine Fumarate (Tavist), and recently Zyrtec is being tried with amazing results. I would contact your veterinarian about a script for one of these medications. Also, dogs with nonresponsive symptoms have really shown improvement with a product called Atopica. Atopica is cyclosporin. This product targets specific cells in the immune system that creates an allergic response. Please visit this site for more information: http://www.us.atopica.com/. You can use atopica and an antihistamine combined to improve his allergic condition.
You and I both know that prednisone is a strong medication and the long term effects can be very damaging. When the allergies flare so severely this may be your only choice. And she can be can be weaned off of it to two or three times a week. If you can use this at the lowest dose possible to produce helpful results then the risk of side effects are also decreased.
Commonly an allergy to a component of the food dogs eat causes the symptoms that you are describing. If you find no results using antihistamines on a longer term basis or the allergies do not let up and you consider them to be more of a chronic year round issue a food trial may be in order. Multiple prescription diets on the market for exactly this scenario. IVD makes Duck and Potato and Venison and Potato just to name a couple. It is less likely for a dog to be allergic to these diets because they are not a common food and it is possible they have never had this particular meat protein. There are other allergy diets like L/A (limited antigen) and Hills Z/D. So, there are several foods you can try. You don't have to put a lot of work into it and they have been proven to give positive results. You just have to find the right one. A food trial will need to last for 8-12 weeks with no other treats except what is in the food. No treats, no table scraps, no mistakes to see if it is a food allergy that is the culprit.
Bathing is also very important. A twice weekly bath if you are up to it, once weekly otherwise to help and remove allergens from the coat and skin. This is best with inhalant allergies but also will help to soothe his irritated skin. I prefer Allerseb-T. It is also possible that she has developed a chronic infection on her feet/skin from the chewing. Bathing with a product called Malaseb from your veterinarian will cover all bases from a potential bacterial to fungal infection. There may be infection on the skin present called staph. Staph lives naturally on the body but can become overabundant when the skin is broken or irritated causing irritation antibiotics are usually needed. Consider adding omega three fatty acids to his diet as this will help improve his skin and coat. This is a great addition to a dogs diet when the skin has issues. It really sounds like she needs an antihistamine to help with the allergic response itself. I would recommend for tonight and until you can discuss these options with your veterinarian that you start the benedryl at a dose of 1mg per pound.
I want you to know that there are still options out there for you and your dog. It is going to take a lot of patience and persistence but it is there and it can help. You may not have 100 percent improvement but you can get close and with the way you both are suffering wouldn't 50% improvement feel pretty good right now?
Allergy testing may be a viable option in your case, but I would definitely consider a food trial first. With allergy testing your veterinarian can draw some blood and send it off to the lab where they will determine what she is sensitive too. With the results you will be able to tell what she needs to avoid and even have an idea when her allergies may start up again especially if the condition is only seasonal. A serum can actually be made to her specific needs and can be given just like in people to help desensitize her to her worst allergens.
I suspect her jitters are from a constant uncomfortable feeling on her skin. It may also be making her a bit grumpy to boot. Hopefully, getting her started on an antihistamine will calm things down abit so that she can be more comfortable.
Please if you have further questions feel free to write back.