What is the ruling regarding blood that flows intermittently for 16 days, then flows again 13 days after it stopped?

A woman must perform ghusl whenever she sees purity (cessation of bleeding). After that, all rulings pertaining to pure women apply to her, so she can pray and fast. If the blood returns, she reverts to being in a state of menstruation. Her acts of worship performed during the period of purity interspersed within menstruation are valid, until fifteen days are completed, combining the days of purity and the days of bleeding. If it exceeds that, she is subject to the rulings of a woman with irregular bleeding (istihadah). If her menstruation returns after thirteen days of its cessation, it is considered menstruation according to the Hanbalis, contrary to the view of the majority of scholars who hold that the minimum period of purity is fifteen days.