What must a mother do who has not fasted for 35 years due to the hardship of herding in the desert, and Ramadan occurred in the summer? Should she make up the missed fasts or feed the poor on their behalf?

Your mother must repent to Allah and make up the days she did not fast, in accordance with His (the Almighty's) saying: "for a limited number of days. So whoever among you is ill or on a journey [during them] then [he must fast] an equal number of days on other days." It is not necessary to fast the missed days consecutively, and she should not resort to feeding the poor unless she is continuously unable to fast, in which case she must feed one poor person for each day.