Thank you for your query.
I can understand your concern for the fever running for 3 weeks. As you have not mentioned the range of the temperature I suggest that you measure the temperature 4-6 hourly and record it. Discuss with your doctor, get your daughter re-examined and re-investigated to know the cause of fever. some investigations which may now be done are Widal
Changing the antibiotic should be left to the treating doctor as he is in a better position to decide. Cifixime will work if your daughter is suffering from enteric fever
I hope I have answered your query to your satisfaction.
Wishing your daughter an early recovery.
Rajiv K Khandelwal