What is the ruling regarding a woman who gave birth to her daughter in Ramadan and breastfed her naturally, but was unable to make up for the days she missed in Ramadan?

You must make up for any missed days of Ramadan (definition). If one delays making up for them, despite being able to do so, until the next Ramadan begins, then a kaffarah (definition) (expiation) of feeding one poor person for each day becomes obligatory, in addition to making up the fasts. However, if one delays making up for them due to a valid excuse until the next Ramadan begins, then only making up the fasts is obligatory, without a kaffarah.