I have a 16 year old daughter she plays waterpolo swimming and netball. lately she complains that she is not coping with school work and sport?

Not uncommon: The teen years are often met with difficult transitions. Many have not acquired the skillset to deal with multi-tasking while confronting the many demands on their time. In the often I would screen her (test sheet) for anxiety/stress and based on that or other findings find a life coach/therapist to help them develop these skills. Family usually can't do it. Good luck.