My daughter had what i thought was a freckle on her back but when it's exposed to sun she gets a larger white patch surrounding it. ?

Hard to know: Tinea versicolor is a fungal infection that appears as spots of various colors: from white to reddish brown to light tan. These lesions can be more apparent after sun exposure because the surrounding skin becomes darker than the involved skin. It is treated with otc anti-fungal agents with "azole" in the active ingredient name. As this is just one possibility, confirming with Dermatologist.