Valerie was born on May 15, 2006 to Michael Rosier and Christine Rosier (née Rondeau). Before going to Hogwarts, Valerie was educated by her parents at the Mansion Rosier in France. Possibly the young girl had been brought up with the old family tradition of witches on mashed superiority of blood and family entirely composed of pure-blood wizards.
In 2017, Valerie went to the Hogwarts School of Witchcraft and Wizardry and was soon sorted into Slytherin. During the banquet, she made friends with two girls her age, Hestia Pucey and Isla Montague, who later would be part of her girl gang. Valerie was very skilled in witchcraft and humiliating others. During a discussion in the Slytherin common room she insulted the family of Isaac Prewett about the purity of blood, however was soon confronted by Albus Potter, which made her angry. She and Isaac changed the spells that yielded an detention with Professor Vector. Since then, Valerie began to hate Albus more than any other.