What is the ruling on making up unobserved days from past Ramadans (20 days), in addition to the days of the current Ramadan (30 days) that were not observed due to pregnancy and breastfeeding, knowing that the previous days could not be made up due to extreme fatigue and the arrival of Ramadan coinciding with school days? Is expiation (kaffarah) required for these days?

She must make up for the days she missed in Ramadan due to a legitimate Shar'i excuse, and it is recommended to do so promptly. It is not obligatory to make them up immediately unless there remains in Sha'ban only enough time to complete them. If the delay was due to a valid excuse, then no fidyah (expiatory payment) is required of her; only the making up of the days (qada') is necessary. However, if she was negligent in delaying the qada' despite being able to do so before the next Ramadan, then she must pay the fidyah, which is feeding one poor person for each day she delayed its qada', according to the majority of scholars. It is not obligatory according to the Hanafis. This also applies to the days she missed due to pregnancy and breastfeeding. If she had an excuse for delaying the qada', then no fidyah is required of her.