Might be fifth disea. Children frequently have a slight temperature elevation without illness. Normal temperature is up to 99.6 degrees. Thermometers are often not accurate. The rosy cheeks occur at the beginning of fifth disease. Children usually develop a rash on the top surface of their arms and thighs. The rash looks like red rings linked together like lace. No treatment necessary. Most clear in about a week.
Viral. From the brief description the #1 illness that comes to mind is erythema infectiosum or slapped cheek virus. It starts with very rosy cheeks and then spreads down the body with a lacy looking rash. It is a normal childhood illness and she will recover fine. It could also be that the fever is simply making her cheeks rosy. If you se worried, make an appointment and see our pediatrician.