My Daughter Has Rash That Is Solid Under Neck, On

My daughter has rash that is solid under neck, on shoulders,down both arms, down her back down to pubic area. The outer parts of the rash is more like hives, big whelps. It itches but not real bad. She is 13 and I have changed nothing in the household. I gave her 25 mg of Benadryl orally. My mother is a nurse and told me not to use Benadryl all cream all over her body and give Benadryl. I have taken pictures but don't know is I can download them so you can see how bad is. Can you help?