Chocolate Lab hives

Question
I have a lab who developed hives 6 days after her vaccines. This is not the first time and she was even treated with a benadryl injection first. She also had a dog food change 2 weeks ago to purina pro plan. She develop hives on friday and we took her to the ER vet where they gave her steroids and benadryl injections. It cleared up until sunday and then came back. The first hives were spiral in nature and were not the same and the next outbreak. This time they looked like pimples ready to burst. they again gave her steroids since we still had her on benadryl. She was even worse on monday so we took her to our Vet and they gave her anoter benadryl shot. Tuesday she went in again even more broke out and they kept her and tried other treatments including an epi injection. She didn't appear to change much so they kept her again today. She has had no signs of respiratory concerns, but is obviously uncomfortable. What would you suggest that the next course of treatment be. Our team of vets are out of ideas at this point. Since she is not under respiratory duress should we just bring her home and treat her topical irritation with oatmeal baths and monitor her breathing. Our vets have said they don't feel this is life threatening but are running blood tests and a hive biopsy to check for cancer. So far all tests except the biopsy are negative. Any suggestions would be greatly appreciated at this point.

Answer
This is a very odd reaction, and I would suspect there is something else going on.  Maybe she got bit by a brown recluse spider or some other type of insect?  I am not sure what she was eating before the ProPlan but it is possible there is a food allergy component too since she is a very reaction-prone dog, so I would take her off the Proplan (as well as all treats and biscuits) and feed her a strict home-made vegetarian diet for a few weeks and see if that helps cleanse her system...you can give her cooked or raw carrots, green beans, broccoli, squash, white potatoes, and sweet potatoes...do not give corn as that can be one very common allergan.  You can give her small amounts of fruits (no grapes) and some brown rice to bulk up the meals.   If you don't want to cook you can get a commercially prepared diet, however, the fresh whole foods would be better for the initial period.

I would also give her Ester C at a dose of 500 mg three times a day, Fish Oil 1000 mg twice a day, MSM 1000 mg twice a day, B50 B complex twice a day and CoQ10 30 mg a day....this will help with the skin, the stress and inflammation of her skin.

Continue the oatmeal baths, but then I would recommend spraying her with black tea or use it as a rinse after the bath as the tannic acids are soothing for the skin.