What is the ruling on praying in undergarments that contain menstrual discharge on the sanitary pad, if the menstruation has reached the stage of istihada (post-menstrual bleeding)?

A woman must perform ghusl (ritual bath) when her menstruation stops and wash whatever menstrual blood has stained her clothes. However, if the bleeding continues, she is considered to have istihada (non-menstrual vaginal bleeding), and she must wash off the blood, tie a cloth over her private parts to prevent its flow, and then perform wudu (ablution) for each prayer. Any blood that exits after that does not invalidate her prayer, even if it stains her clothes. As for the menstrual blood on the sanitary pad, it must be washed off due to its impurity, unlike the blood of istihada, which is excused due to necessity.