What should a woman do who vowed to slaughter a sheep every year while she was a polytheist, and did not fulfill her vow, then Allah guided her?

Scholars have differed on the obligation for a disbeliever to fulfill vows of devotion if he embraces Islam:

The majority (Hanafis, Malikis, and Shafi'is): He is not obligated to fulfill it. It is recommended according to the Malikis and Shafi'is, but not recommended according to the Hanafis. The Hanbalis: His vow is valid, and he must fulfill it after embracing Islam, citing as evidence the hadith of Umar ibn al-Khattab, may Allah be pleased with him, with the Prophet, peace and blessings be upon him.