She must be allergic to something, as my dog had the same thing, she's allergic to flees, and had really bad rashes all over her head, ear's and back.
Dog's can get pretty bad rashes or bump's on their skin when they have an allergic reaction. She might have hive's, but really I'm not sure. Here's a link for more information, this might help you. http://www.pet360.com/dog/health/hives-in-dogs/VTPRBYEAEE6Qn6YdlF6pSw?utm_source=NPP&utm_medium=NPP&utm_campaign=NPP+Redirects&extcid=NPP