Hello, I Just Got A Message From My Daughter That

Hello, I just got a message from my daughter that my 15 yr old granddaughter got an itchy rash that started on her back and neck and now on legs(thighs) and fore arms as well. Looks to have some swelling or blisters(raised rash) from the pics. They took her to the Urgent care and was given a steroid short and a prescription(I don't know what she was given). said it is working some now. She had not eaten anything different or done anything different except had what looks like a mosquito bite on her calf. Not sure that is what that is. Any ideas what could have caused this ?
This is pretty vague but a sudden rash is odd for her.