Your daughter's pediatrician
could certainly be right that these symptoms are related to some sort of viral infection, as this is definitely one of the most common causes of rashes in this age group. However, the fact that there has been no fever
or other clear signs of a viral infection (like runny nose or cough) is somewhat perplexing, because classically these “viral rashes" appear a few days after the other symptoms, such as fever, have already started.
Another possibility would be an allergic reaction, which could be related to something your daughter has come into contact with. Even though you can't recall using any new products in the home, for most allergic reactions, an offending source is never really found. If you notice that the rash responds well to the anti-histamine then that might be further evidence that this is an allergic type rash.
I would suggest going back to see your daughter's pediatrician again, now that this has been going on for a few days. Sometimes, the only way to arrive at the correct diagnosis in these cases is to have your doctor
look at the rash a few different times, so that they can see how it changes and evolves over time. Book an appointment today.