Does the vow of a mother who vowed to sacrifice a cow for her son's recovery, and who has recovered, fall due to her financial inability to fulfill the vow and her son's refusal to contribute to its costs?

A vow (Nadhir) must be fulfilled if it is made for Allah Almighty, as the Prophet (peace be upon him) said: "And let them fulfill their vows," and "Whoever vows to obey Allah, let him obey Him." If fulfilling it becomes impossible due to lack of funds, the vow is annulled and an expiation for an oath (kaffarat yameen) becomes obligatory, as the Prophet (peace be upon him) said: "The expiation for a vow is the expiation for an oath." And whoever vows a vow he cannot fulfill, its expiation is the expiation for an oath. As for specified vows, if they are acts of obedience and are within one's capability, they must be fulfilled. If they are not within one's capability, then an expiation for an oath is due. However, if they involve disobedience, it is not permissible to fulfill them, and they are not considered valid. If they are permissible and within one's capability, the apparent ruling is that they are valid and require expiation. If they are not within one's capability, then expiation is due.