Praise be to Allaah.
We put this question to Shaykh Muhammad ibn Saalih al-‘Uthaymeen, who answered as follows:
Praise be to Allaah, and peace and blessings be upon the Messenger of Allaah.
Perhaps she thinks that doing these rituals does not contradict Islam, so first of all call her to stop doing these things. If she agrees, then this is what you want. If she does not agree, tell her: “If you do not stop doing these rituals, then there is no marriage between us (i.e., threatening divorce).” Of course, if she wants to stay with her husband, this will make her come to Islam. If she refuses, in spite of this threat, then there is no marriage and he has to leave her. And Allaah knows best.