It looks like eczema but while it might not be that; people who have been tanning more than their body/skin can handle can induce common light sensitive skin ailments like basic skin rashes, dry patches from overly drying from tanning and not using enough moisturizer and even often known to induce cold sores if you happen to have a history with them.

She shouldn't tan so frequent and lube her body up with some kind of moisturizer. Maybe she should do a gokkun.