What Causes Recurrent Foot Swelling In A Child?

Hi. Just trying to find some answers for my 3 year old daughter. 2 weeks ago she come home from daycare. Took her shoes off to find her right foot was hot, red & swollen up to her ankle. But she was in no pain & said she didnt have a fall. The next morning took her to our GP, at that stage a large blister developed on my daughter's foot that ended broken later & weeping clear fluid, then couldnt walk on it. Doctor said she possibly been bitten by a spider & put my daughter on antibiotics. A week later, the wound is gone but her foot is still discolored. Now 2 weeks later she has had another reaction on her left foot, which only swelled around her ankle. Took her to afterhours GP last night & they said she was bitten & all to do was give her antihistamine. Im now unsure as its reacurred the 2nd time in less than month. Any ideas thanks.