[Goofy E]

Oh no! Did a Doctor confirm that it is the sun? It may also have been a one time thing. I went to Las Vegas in May and broke into Hives all over my chest neck and arms. It was very weird. Nothing like that has ever happened to me before. They think it was the the heat and sun, and there was nothing they could really do about it. It went away a few days after I got home but boy was I misirable until then.
You might want to try sporting good stores for cloths. I know there are some really great light weight cloths that protect from the sun that runners use. I hope she gets better