What should a wife do if she is unable to make up for missed days of Ramadan from last year due to pregnancy and breastfeeding, based on her doctor's recommendation, and what should she do if this excuse continues until after next Ramadan?

Allah has made it easy to make up for missed fasts of Ramadan (definition) for those who broke their fast due to a legitimate شرعي excuse. It is recommended not to delay making up these fasts except when absolutely necessary. Whoever delays making up a fast without an excuse until the next Ramadan begins is sinful, and must make up the fast after the second Ramadan. They may also be required to pay a fidyah (definition) (expiatory payment) of feeding a poor person for each day. As for whoever delayed it due to an excuse, there is no sin upon them, and they must make up the fast. Scholars have unanimously agreed that delaying the make-up fast of Ramadan until after the next Ramadan is impermissible unless there is an excuse. Whoever does so without an excuse is sinful. Ibn Uthaymeen was of the opinion that simply making up the fast is sufficient for one who delayed due to an excuse, and they are not required to feed the poor.