Are the prayers and fasting of a woman who used to perform ghusl al-nadhafa (cleansing bath) with the intention of purification from menstruation, then perform wudu, and consider herself pure, valid? And if they are not, what should she do, given that she has been doing this since puberty?

If a woman performs ghusl (ritual bath) with the intention of purification after the end of her menstrual period, then her ghusl is valid, and the use of cleansers does not harm it. However, if she performs ghusl at the beginning of her menstrual period and does not perform it after it ends, then her ghusl and prayers are invalid. She must make up the prayers she performed after menstruation. Her fasting is valid because purity is not a condition for it, but she is not permitted to fast during menstruation.