My mother is refusing further chemo treatment. what can happen?

Progression?: If she has cancer that is still in her body and the chemotherapy is being used to slow tumor progression or spread then stopping the chemotherapy will allow it grow, spread, worsen. If the chemotherapy was after tumor removal and only for additional insurance to prevent tumor cells from recurring, then she may b fine. If she incompetent and understands the pros & cons then all u can do is support.