Offering sacrifice for anyone other than Allah is considered an act of Shirk Akbar (major form of associating others in worship with Allah). The Prophet (peace be upon him) cursed those who offered sacrifices for anyone other than Allah. So offering a sacrifice is not permissible in the case mentioned above for seeking a cure for your wife. The permissible treatment should be through lawful medication and Shar`y (Islamically lawful) Ruqyah (reciting Qur'an and saying supplications over the sick seeking healing). You should advise your wife not to offer sacrifices to anyone other than Allah and to pursue the permitted ways of treatment. May Allah grant her recovery and guidance.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.