Is a mother obligated to fulfill her vow to slaughter a calf after her daughter's divorce from an atheist husband, especially since she does not have sufficient funds?

If a Muslim vows an act of obedience to Allah Almighty, it becomes obligatory to fulfill it, as Allah Almighty says: "And let them fulfill their vows," and as the Prophet, peace and blessings be upon him, said: "Whoever vows to obey Allah, let him obey Him." A vow contingent upon a condition becomes obligatory to fulfill when the condition is met.

If the mother vowed to slaughter a calf upon her daughter's marriage, and she did not specify a particular husband, then she must fulfill it as long as the marriage has occurred and as long as she is able to fulfill it.

If she is temporarily unable to fulfill it, and her inability is expected to cease, she may postpone it. If her inability is not expected to cease, then she must offer an expiation for an oath, as the Prophet, peace and blessings be upon him, said: "The expiation for a vow is the expiation for an oath."