Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am very sorry to hear about poor Amy being stung.
I know she doesn't want the area touched but please check the area closely to make sure the stinger is out. The longer the stinger stays embedded the more venom will be injected. If the stinger is still present remove it with tweezers or the edge of a credit card.
Then treatment is based upon stopping further allergic reaction with antihistamines like Benadryl and sometimes cortisone if the reaction progresses.
Is her breathing normal?
Any vomiting or diarrhea?
Any facial or neck swelling?
I know you gave her an antihistamine, was it Benadryl? I want to make sure you gave an appropriate dose. We recommend Benadryl (diphenhydramine only don't use the combination products with decongestants or acetaminophen 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. You'll need to give it for at least 72 hours (3 days) to allow the allergen time to clear. If you stop too soon the reaction will recur.
Dogs take a really high dose of antihistamines compared to people, so don't let the amount worry you. They require more than we do. This may make her a little sleepy.
You can also apply a cool compress to the sting area and/or give her a cool water bath with an oatmeal based shampoo to soothe her skin. The cool water will close skin capillaries which slows venom being absorbed systemically, and allows it to break down locally, and this will also reduce inflammation, and oatmeal reduces inflammation. Lather the area gently, let it sit for several minutes and then rinse with cool water.
Then you can pat the area dry and apply a little cortisone cream (Cortaid or any generic cortisone is fine) to the sting area.
And then you'll need to watch her closely for any progression of symptoms. That includes difficulty breathing, vomiting or diarrhea.
The swelling/redness/pain should resolve slowly over the next 12 to 24 hours.
In extreme allergic reactions they can get shocky and collapse but you should see difficulty breathing and vomiting/diarrhea first. Those types of severe reactions are very rare.
Most reactions are managed just fine with antihistamines alone.
If you notice progression of her symptoms don't wait, have her checked on an emergency basis.
If you'd like you can have a veterinarian check her now. They can give a cortisone injection which will lessen symptoms faster. But if she seems to be stable then I would just closely observe her.
Please let me know if you have any further questions.