Fever and no symptoms ?

My 3 year old has had a fever for 5/6 days. It’s been all the way up to 104. We’re in the hospital because of it. She hasn’t wanted to eat or drink. She has had no other symptoms except for fatigue and body aches/pains. She’s tested negative for strep, flu, mono, and COVID. Testing for cat scratch fever( she has a scratch ) & checking for tick born illnesses. They said her labs look good except for sum inflammation. What could be cause of this ? Has anyone had this happen before ?