What is the ruling regarding the missed prayers from before I knew of the obligation to make up the Dhuhr prayer with the Asr prayer after performing ghusl from menstruation at Asr time?

If a woman's menstruation ends at the time of 'Asr, she must perform ghusl and pray both Dhuhr and 'Asr. This is the view of the majority of scholars. Accordingly, she must make up the Dhuhr prayers for the period during which the aforementioned state occurred. If she cannot ascertain the exact duration, she should continue to make up the prayers until she is reasonably certain that her obligation has been fulfilled.