I think it is a mosquito bite. my boy had this a few times from different places, in school and sometimes near our home. He just gets a very bad reaction from bites. You can try MyLO itch relief patch from shopee. It helps to reduce the size of the wound. And you can also get those itch relief foam from PD if it gets very itchy. for my boy, this usually takes about 1 to 2 weeks to heal.
As for prevention, maybe request for her teacher to reapply the repellent every few hours.