Hi,
I am sorry for the health problems your daughter is going through.
Fever is causing weakness and perhaps loss of appetite even not consuming water.
This is causing her stomach to produce more acidic fluid. This can get back to throat and causing bad smelling.
Furthermore, if she doesn't take proper care for her
oral hygiene, then, the smelling is more intense.
Next, fever if viral is also associated with
gastrointestinal infection, and
indigestion of food., which makes the smelling worse.
So, give her lots of fluids and antacids and probiotics to keep rehydrated, stabilize stomach pH and intestinal flora.
If still no improvement, should consult with her physician for further evaluation and a more specific treatment.
Wish fast recovery.
Dr.Albana