Even if you’re not actively allergic, Benadryl is often quite helpful in these situations. I’ve used it to pretty good effect for bee and wasp stings, ant stings, and deer fly bites. Less helpful with black flies or mosquitos, but as mentioned mosquito bites can be cooked out (I used to use a cigarette for that when I smoked, now any hot metal object will do).
For swelling like you describe, I usually take 50 mg of Benadryl and find it quite helpful, but it can make you quite drowsy / swim my headed. Of course, I am a 260 lb man, so that may be too much Diphenhydramine for your wife, maybe start at half that.