What Causes Persistent Fever While Treating An UTI In A Child?

My daughter turned 3 june 2nd. She went to the er yesterday where she was diagnosed with an uti. The gave her a 24 hour antibiotic injection an prescribed a antibiotic by the name of cephalexin 250/5 mg susp she takes 7ml twice daily. .she started them this morning. She has had fever started at 101.6 under the arm so add one it s really 102.6 befor er visit an at er had temp of 102.6. So my thermometer was acreit. The got the fever down an I ve been using Tylenol age2-11 it recommend by weight to give oral 7.5 ml .it s worked till now an she has a fever of 103. Under the arm with the same thermometer used before er visit so it 104. Is this normal . after having injection of antibiotic at 7pm yesterday at er an started taking oral antibiotics around 12 noonish today as well as the second does at bed time in between 8:30pm an 9:00pm