What is the ruling on prayer for a woman who is 54 years old and whose menstrual period was regular for five days every 21 days, then became irregular, coming for a long time, then stopping for a few days and returning?

The blood a woman sees after the age of fifty is considered menstrual blood, according to the preponderant opinion. The maximum duration of menstruation is fifteen days, and the minimum period of purity between two menstrual cycles is thirteen days, according to the Hanbalis. If the bleeding exceeds fifteen days, or the period of purity is less than thirteen days, then she is considered to be suffering from Istihada (non-menstrual vaginal bleeding). She should then refer to her previous habit, observing five days of menstruation out of every twenty-one days, and then perform Ghusl (ritual bath). Any bleeding beyond that is Istihada. In this case, she should take precautions and perform Wudu (ablution) for each prayer after its time has begun. She is then subject to the rulings applicable to women who are pure.