My daughter has had brown discharge for 3 weeks on thursday, very light & got on day due on period, is this normal?

No: Abnormal discharge for 3 weeks is not normal. What is the age of the patient? Please provide more details to help you better.

Spotting: Irregular bleeding is one of the most common problems obgyns treat. If this is one time problem it usually resolves on its own. If this is a recurring problem you should be evaluated. Infections ; hormonal changes can cause spotting. If there is a concern for pregnancy then do a home pregnancy test . There are many options available to help regulate the menstrual cycle. Schedule a visit.