Post Viral Rash v. Hives?

This morning Ashley suddenly developed a rash that is identical to a post-viral rash she had last time she was sick (thousands of tiny spots, not raised, all over her body from head to toe. She has had a super runny nose for a week but has been otherwise well.

The rash came about 5 mins after her breakfast. How would I know if it is hives?? She hate her usual breakfast and hasn't reacted to the food before.

Is it safe to assume it is a post-viral rash given the fact she has had a runny nose? Or would the sudden onset indicate hives??