She pressures Leila to allow, indeed, to persuade, Reza to take a second wife who will be able to bear him a son. Reza, you see, is Mother's only male child, the only hope for producing an heir. All the while, Mother keeps up, and steps up, her psychological campaign to get Leila aboard the second-wife idea. She knows Reza never will go for it unless Leila doesn't merely accede but actively promotes it. While Leila is obviously from an educated and wealthy background, she is no match for forceful Mother.
Mother is a fearful character.
No doubt due to her upbringing, Leila bows to Mother's wishes, and the search for another bride begins. Leila and Reza ride together to meet the first prospective child-bearer. They laugh merrily as though this were a joke. The meeting goes badly, and, when Reza and Leila meet afterward, they are amused again. When they arrive home, Mother telephones.