How does a woman fast if the duration of her menstruation suddenly increases during Ramadan?

If the duration of menstruation exceeds its usual length, a woman remains in a state of menses and abstains from prayer and fasting, unless the duration of the bleeding exceeds 15 days. If it exceeds this period, she is considered to be in a state of istihada (non-menstrual vaginal bleeding) and should act as a woman in istihada.