Fever for 6 days in 7 yo child...negative for everything...what could it be??

My 7 yo daughter is healthy height and weight. She has viral asthma that is well controlled with rescue inhalers. She did have strep throat 4 times last year, but her ped believes that she could have had a "carrier" in her class as she has not had an infection since.

She started with a fever on Thursday evening (6 days ago) and a mild sore throat. No coughing, but we began her steroid inhaler per the asthma action plan. By Saturday, she still had a fever of 100.8-101.2 so we took her to urgent care for a strep test. Strep and flu tests were negative. By Monday, fever was still around and coughing had begun, so we added in her albuterol inhaler. The cough was relentless, but does seem to calm down with albuterol. We could not see our pediatrician as she is out on Mondays, but the doctor we saw re-tested for flu/covid/strep and tested for a UTI and said it was all negative, so probably viral.

I am at my wit's end. What else can I ask to be tested? She has never had a fever last this long, even when she was hospitalized with RSV as a child and with the flu last year. I will be calling the office as soon as they open, but I would appreciate any direction or questions I could ask of the doctors. Again, she has never had a fever that lasted this long, and I am very worried. Thank you!