DD got some bites like this yesterday. Oddly enough, the mosquito bites she gets in our backyard look like normal bites. The mosquito bites she got last night at the boat club down on the shoreline are HUGE, and so were the mosquitos -- they were visibly larger than the ones near our house.
She has fair, sensitive skin anyway, and again with the odd . . . last summer whenever she played outside, she froze rigid every time she saw a bee. Completely petrified. It was very out of character for her. She has no bug phobias, has never been stung, and is generally very gung ho about meeting new critters. I wonder if she's allergic to bee stings because my grandmother, father, and sister all are (and physically she takes after all of them, too).
I iced her welts and gave her some arnica (this was for other bumps and bruises, but it might have helped), and the swelling went down a lot over the course of the day.