Suggest Remedy For Red Blotchy Marks On Exposure To Sun

When the back of my daughters legs are exposed to the sun she gets red blotchy marks (almost cheetah looking spots) on the legs. It's just in the back of the lower legs and they do not itch or hurt her. The skin stays flat too, it does not get raised at all. I notice it usually appears in the summer when the sun is really hot. My daughter is half African American and half Mexican (just thought I would mention that). Can you tell me if you have ever heard of anything like this?