Suggest Treatment For Rashes On Chest In Kid

hello, my 10 year old daughter got a rash type spot on her chest during a camping trip at the beach. it was raised and red water type blisters. once it clearen up it left white spots in the area. this happened about 2 years ago and there has not been any problems just the change in her pigmentation where the rash was. she was recently exposed to the sun without sunscreen and the area and water blisters have appeared it is red and itchy. i have had our peditrician and dermotologist look at it with no answers. im concerned