Does the questioner act in accordance with the hadith of Aisha or the hadith of Umm Atiyyah in determining purity from menstruation, especially since her menstruation is irregular, and she notices the discharge of something resembling blood after performing ghusl on the eighth or ninth day?

If the blood seen after purification is normal blood, it is menstruation if it occurs within the possible time frame. As for yellowish and brownish discharge, they are considered menstruation if they occur within the period of one's customary cycle or are connected to blood; otherwise, they are not. One must perform istinjā' (ritual cleansing) from them, and if their discharge is continuous, then your ruling is that of a woman with istihāḍah (non-menstrual bleeding). There is no contradiction between the hadith of Umm Atiyyah and Aisha, may Allah be pleased with them both; for Aisha's yellowish and brownish discharge is interpreted as that which was connected to blood or occurred during the period of her customary cycle, and Umm Atiyyah's hadith is interpreted as referring to what occurs after the completion of the customary cycle and purification.