Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that Zoey has swelling and a rash around her eyes, I'm sure that is uncomfortable for her.
The most common cause of these symptoms is an allergic reaction to something. It could be an insect bite or sting, or or could be related to pollens or mold spores in the air, or a food allergy. Rarely it is due to a contact irritation (getting something in her eyes).
Sometimes with a slower onset of symptoms this can be related to a demodex mite infection.
Finally some autoimmune (body attacks itself) diseases (Pemphigus for example) can affect the area around the eyes with lesions that include swelling, red skin, sometimes blister like lesions, erosions and crusts.
Because allergies are the most common cause you can try some things at home to see if you can help her. You can use a combination of antihistamines and high doses of omega-3 fatty acids to help. In combination fatty acids and antihistamines work synergistically, much better than either one alone. If her symptoms came up pretty suddenly and seem to worsen seasonally I would think that inhaled allergens are a part of her problem.
You can try:
1)Benadryl (diphenhydramine only don't use the combination products with acetaminophen or decongestants as they can be toxic for dogs) at a dose of 1mg to 2mg per pound of body weight or one 25mg capsule per 15 to 25 pounds of body weight orally every 8 hours. I know that you tried Benadryl, but I wanted to make sure that you gave an accurate dose, and used the right formulation (without decongestants or acetaminophen).
OR 2)Claritin (loratidine) at 5mg per 25 pounds of body weight once or twice daily.
OR 3)Hydroxyzine at 1mg per pound of body weight orally every 8 hours.
OR 4) Chlorpheniramine at 4mg to 8mg per dog once or twice daily.
OR 5) Zyrtec (Cetirizine hydrochloride) at 1/2 mg per pound of body weight orally every 24 hours. That would be one 10mg tablet per 20 pounds of body weight. Make sure it is NOT the formulation with a decongestant (such as Zyrtec-D) because dogs cannot tolerate decongestants.
Some dogs do better on one antihistamine rather than another. Give the one you pick a week trial and if it isn't working try another. In general I see Cetirizine help the most dogs, but every dog is different so I gave you several to try. Be aware antihistamines can cause sleepiness or hyperactivity in some dogs. These side effects do wear off with repeated use.
Omega-3 fatty acids are fish oil products. 3V by DVM or Derm Caps ES are good brand name products. Use the high end of the dosing schedule for your pup's weight. I recommend a dose based upon the EPA portion (eicosapentanoic acid) of the supplement as if we do that the rest of the supplement will be properly balanced. Give her 20mg of EPA per pound of body weight per day. For example an 80 pound dog could take 1600mg of EPA per day.
Cool water compresses may help reduce swelling and inflammation. The water rinses off allergens in her hair and the cool temperature soothes itchy skin.
Food allergy is very possible with her as well given the location of lesions and if she seems to be itchy all year round. Dogs can develop allergies to any protein or carbohydrate so even if she is only fed one thing that can be what she is allergic to. Dogs with food allergies tend to lick and scratch their paws, face and ears the most, but any of the "allergy reactive areas" can be affected.
I don't know what sort of diet change you made. Make sure that the food that you put her on is a true hypoallergenic diet. The trouble with "limited ingredient" or "low allergy" pet store brands is that the same machinery is used on multiple lots of food without sterilization cleaning in between. So for example even if a food says it has salmon and rice if the previous batch had beef and corn then you will get traces of those ingredients in your bag of food. Not a big deal if your dog isn't allergic but a waste of money thinking that the food was hypoallergenic and not good for your dog if those happen to be allergens for your dog. The veterinary brand true hypoallergenic foods are more expensive because it isn't cheap to thoroughly remove all traces of a previous food mixture from the machines used to process food.
Generally what I recommend is trying to clear the skin and then adding one food item (chicken, beef, corn wheat etc) every month to see what they react to. Then we can find a regular food to try. As far as permanent diets I do tend to stick with Purina Pro Plan brands or Nature's Recipe as I find those rarely if ever have cross contamination. Purina Pro Plan Turkey and Barley or Nature's Recipe Vegetarian or Venison are pretty good products. I know that this isn't easy from personal experience (my dog is allergic to wheat) and it is time consuming, but worth it.
If you choose to try testing/treating her for a food allergy I recommend that you try a true hypoallergenic diet like Hills z/d or Purina Veterinary Diets HA. No treats, flavored medication or bones while on the diet and it must be used for a least 12 to 16 weeks to see the full effects. You should see some improvement in 6 to 8 weeks.
If she is rubbing her face on things or pawing at her face I highly recommend placing an elizabethan (lampshade , cone of shame) collar on her. The more she rubs the more traumatized her skin will be and chances of causing a corneal ulcer or a secondary skin infection increase the more she rubs.
If she isn't significantly better in a few days then I recommend having your family veterinarian take a look at her.
Please let me know if you have any further questions.