How did Sultana force Kareem to sign an agreement to not marry another as long as she was alive?

Sultana took her passport and a letter allowing her to travel that she forged and flew to Dubai where the children were attending a camp. From there, Sultana took a commercial flight to London. Once in London, Sultana and the children traveled to Zurich where she withdrew money from her son's bank account. Then they returned to Paris where Sultana rented a house. A few months later, Sultana called Kareem and agreed to meet him. Sultana told Kareem she would only return to him if he promised to sign a contract agreeing to never marry another woman while Sultana was alive. Kareem agreed and Sultana eventually returned with the children.