What she was referring to was the matrimonial matters between Fei'er and Mo Ziqi after their grand wedding.
Fei'er was only twelve years old, still a child. Although she had received better nutrition over the past year, and Cai Wei had been providing space-grown food to her family all year round, leading her to develop well and look like a girl of fourteen or fifteen, a child is still a child. Her body had yet to develop fully, and her first menstruation hadn't come. If Mo Ziqi couldn't contain himself one moment and did that thing to her, it would surely cause harm to Fei'er's body.
Therefore, one day when Empress Dowager Mo was not around, she sent away the servants, and with much hesitation, conveyed her thoughts to Old Madame. In essence, she hoped that Old Madame could speak to Mo Ziqi, suggesting they wait until Fei'er reached the age of fourteen or fifteen to perform the conjugal rite.