Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your girl Yoshi was stung by a bee. It sounds like she was treated normally with an injection of an antihistamine, which should counteract allergic reaction symptoms from the sting.
Possible side effects from a sting include localized pain, swelling, redness and an itchy feeling at the site of the sting, which can progress to generalized hives and an all over itchy, uncomfortable feeling. More severe systemic effects include difficulty breathing, throat swelling and edema, possible pulmonary edema (fluid in the lungs), vomiting or diarrhea and rarely liver damage.
The localized swelling/redness should resolve slowly over 12 to 24 hours.
In extreme allergic reactions they can get shocky and collapse but you should see difficulty breathing and vomiting/diarrhea first. That type of severe reaction could cause brain
damage due to sudden changes in blood pressure and brain oxygenation but they are very rare.
I usually continue treatment with antihistamines for 72 hours as I find some dogs relapse with symptoms if we don't treat long enough.
Her changes in mental awareness and acuity are not what I would normally expect to see secondary to a wasp sting, especially if she has no history of collapse after the sting. It is possible that there is something else going on, or that she suffered from an elevation in blood pressure causing brain bleeding
or threw a blood clot which blocked blood flow and oxygen to her brain and she is suffering from the effects of a stroke. Strokes are not common in dogs but may occur after a stressful event such as a systemic allergic reaction.
Whatever is going on with your girl this is not what I would expect to see as a usual reaction to a wasp sting. Referral to a veterinary internal medicine specialist or neurologist would be reasonable now.
Please let me know if you have any further questions.