What Causes Sunburnt Cheeks And Blotchy Arms?

My daughter is 5 years old and woke up with a rash on her right cheek that was hot to the touch. She acted fine and didn't have a fever. As the day progressed, it moved across her face. 2 days later, it is only on her left cheek now (still hot to the touch) but is also now on her arms. It looks like she has sun burn on her cheek but her arms are blotchy. Should I take her to the doctor or just let it run its course?