Is it permissible for a woman who broke her fast in Ramadan due to childbirth and breastfeeding, then became pregnant and gave birth in the following Ramadan, to pay money instead of making up the fast?

A woman must make up the days she missed, even if it is after the second Ramadan, because her excuse for delaying the make-up between the two Ramadans is valid. And if making them up consecutively is difficult for her, there is no harm in her delaying it until the second Ramadan.