What is the ruling for a woman who has forgotten her established menstrual pattern while the blood observed is black?

Primary text

If a woman has forgotten her established pattern and the observed blood is black, and the ruling dictates that abstinence begins from the start of the month, then she should observe the minimum duration that a forgetful woman observes, even if the blood observed is initially red. She does not transition to treating the black blood as menses until the pattern repeats and is confirmed to be menses. Once confirmed, she must then make up (Qada) any obligatory fasts missed during those confirmed periods.