What should my mother do about making up for three Ramadans of fasting that she missed due to postpartum bleeding (nifas), then a heart surgery, and taking medication thereafter, especially given that 17 years have passed since then?

The mother is obliged to make up the three months she missed due to a valid excuse. She is also obliged to pay an expiation for delaying the make-up if she was aware of the impermissibility of the delay. This expiation is approximately 750 grams of the staple food of the country for each day, to be given to the poor. However, if her failure to make up the fast was due to ignorance or forgetfulness, then there is no expiation upon her. She is not required to make up the fast consecutively.