What should a woman do if Ramadan came and she did not fast due to postpartum bleeding (nifas), and she did not make up what she missed until another Ramadan came?

A woman is obligated to proactively make up any missed fasts before the current Ramadan begins. If she broke her fast due to an excuse and that excuse persisted until Ramadan commenced, she is not liable for expiation. However, if the excuse did not persist, she is liable for expiation along with making up the fast.