She (age 12) Went To Doctor Monday With A Red

She (age 12) went to doctor Monday with a red rash all over her face and throat swollen. Doctor checked and she had temp of 100.2. Strep came back negative but she was put on antibiotics. Rash is gone but She continues to have a fever hovering at 100.3 unless taking Tylenol. Went back to doc today and tested negative for mono. Sent her home taking mucinex and to drink a lot of water. Should she have gotten blood drawn?