Ruling on Someone who Vowed to Make an Animal Sacrifice but didn’t Fulfill the Vow

A woman vowed that if her brother-in-law married another woman on his second wife, she would make a sacrifice (slaughter an animal). He got married, but she didn’t sacrifice. Rather, she did the (known) atonement of oath, because she sees the vow as an act of disobedience to Allah (a vow of disobedience). He says: what is obligatory upon her now, fulfilling the vow or is the atonement of oath enough?