This is not a high fever, especially rectal.
I know there comes a point though when you should not use motrin or tylenol past so many days. So, I would say unless she acts like the fever is bothering her, do not treat her anymore. Sometimes a virus can take a while to get over, and, there is nothing you can do for a virus besides make them comfortable until it passes.
Now, that said. My second daughter had a UTI with no other symptoms than a fever. But, she was crying a lot. She was only a few months old, so, harder to communicate with. Is your daughter acting like it hurts to pee? This will not show up in blood tests. They had to do a urine test. Simple, they taped a bag around her vagina, and, the next time she peed the bag collected it. We had to wait at the lab to "wait" for her to pee. But, her urine tested positive for the UTI. The pedi had told me that many times, an unexplained fever that lingers could be a UTI as there are no other symptoms such as coughing, runny nose, etc.