When my brother was 11 there was an epidemic of measles in his age group because they were vaxinating too young. He was one of the unlucky ones to get it. He was miserable and unable to move from the sofa for a week. I seem to remember him itching and spiking a pretty high daytime temp. (I was 8 at the time though, so my memory of this may not be accurate.)
I wanted to add that when I was in college I got a rash that sounds like the one your baby has. It started behind the ears and knees and then spread across the trunk and eventually did cover my face. I had a very sore throat and when I went to the doctor they could not determine what I had. They said it was a virus with a rash and they made up a technical sounding name for it but when I looked it up it just meant red rash accompanying a virus.
If you are concerned you should call your doctor. I would also start giving her a teaspoon of colloidial silver every few hours for the next week. Once it builds up in her system it should be able to suffocate the virus.
Good luck to you. I know how miserable everyone is when a toddler is sick. It breaks your heart.
Let me know what you find out.