What is required of a woman who vowed to slaughter a sheep and fast for a full year upon her son's recovery, given that she has become old and is unable to fast?

Vowing is discouraged (makruh), but whoever vows an act of obedience must fulfill it. The woman in question must give a sheep in charity and fast to fulfill her vow. If she is permanently unable to fast, then an expiation for breaking an oath (kaffarat yamin) suffices. Some scholars hold the view that feeding a poor person for each day of the year is also obligatory, in addition to the expiation for breaking an oath. If one vows an act of obedience that they cannot perform or become unable to perform, they must offer an expiation for breaking an oath. If the vow was to fast, there are two narrations from Ahmad: the first is the obligation to feed one poor person for each day, and the second is that nothing else is obligatory besides the expiation for breaking an oath.