She vowed to slaughter a sheep every year but did not fulfill it; what is required of her?

Question:
May Allah reward you with good and do you well. From the Qaryat region, a listener sent a message, using the letters of his name as a code: Hasan al-Balawi. He says: My mother made a vow following the illness of one of her daughters, saying she would slaughter a sheep as a sacrifice every year. The girl recovered from this illness, praise be to Allah, and about twenty-two years have passed since her recovery. She did not slaughter during these years, and she began slaughtering in the year 1456. Now she asks about the ruling on the past years, whether she was forgetting the vow or remembering it. May Allah reward you with good.

Answer:
This vow is a debt in her conscience. If she intended to slaughter a sacrifice every year, and she vowed to slaughter a sacrifice every year, then this is obligatory for her, based on the saying of the Messenger (peace and blessings be upon him) If she made it obligatory upon herself to offer a sacrifice every year, she must slaughter. If years have passed and she did not slaughter, she must make up the years that have passed, slaughtering for what was missed, and she must apply to it what applies to sacrifices regarding eating, giving, and donating. Additionally, along with making up what was missed, she must expiate for the delay with the expiation of an oath.