Winterwillow was born to Whitecliff, the unicorn Overseer of Stable 83, and Snowfall, the deer population's elected "princess." Her parents love story always fascinated her. Snowfall was a young doe who fought for the rights of deer and aimed to overthrow the unicorn Overseer, Shearwater, a brutal and cold-hearted leader who constantly abused and took for granted his deer residents. Whitecliff was Shearwater's son, whom had never agreed with his father's cruel methods and instead wanted a harmonious future with deer and unicorns side by side. Their meeting was inevitable. Together, they planned a future in which their entire stable was united, and eventually grew to care for one another.

From their eventual marriage came Winterwillow, the first half deer-half pony born in Stable 83 in over a century. Her birth halted the brewing civil war in its tracks. Winter was seen by the deer as the manifestation of hope for a brighter future. While the unicorns were not keen on the idea of a half-deer child, lineage and inheritance was very important to their way of life. She was Overseer Whitecliff's daughter and would become Overseer in her own turn. She would be their leader, whether they liked it or not. And so, both deer and ponies were committed to following her.

Before marrying Snowfall, Whitecliff had been betrothed to a unicorn mare named Mascarpone. After he broke off his engagement with her to follow his heart, she went on to marry another and have a foal of her own. As penance for his betrayal to Mascarpone, Whitecliff promised his daughter to her son, Buttermilk Sky. Winterwillow was raised very closely with Buttermilk, as they were to be married one day. While she had always been deeply in love with him, he did not seem to feel the same way for her. Regardless, they worked and trained towards eventually leading the stable together, and became very close friends. 

When Winter was still a young filly, her mother was murdered by Oleander, her father's best friend whom she had always called uncle. He was also the father of Buttermilk, Winter's betrothed. He had never been happy with Whitecliff's decision to marry a deer, and only grew more angry as stable laws were changed to allow the deer more freedom. This anger festered until the night Oleander could no longer sit by and watch his beloved stable spiral into madness. He needed to take matters into his own hooves. Had the security alarm not triggered and immediately locked down Winter's bedroom where she was asleep, it is feared he would have tried to kill her as well.

Snowfall's death threatened civil war once again. During the announcement, when the entirety of the stable was gathered in the main atrium to hear the news, fighting broke out between deer and ponies. Young Winterwillow, barely old enough to have a cutie mark (had it been possible for her to earn one), stepped up to the front of the stage and publicly addressed her stable for the first time. She did not yet understand what happened to her mother, but knew Snowfall wouldn't have wanted the stable to be fighting. Winter begged her residents for peace, urging them to remember her mother lovingly and keep her hopes and dreams in their hearts.

From that day on, the deer referred to Winter with the same title they had once used for her mother, Princess. As years passed and Winter worked diligently to make the stable a better place to live for both deer and ponies, the unicorns slowly began to adopt this title for her as well. It was never something that Winter enjoyed being called. It was her mother's title, and she felt that she had not yet done enough to deserve it. Every day of her life was dedicated to the progress of Stable 83. She was making real change, change that her mother and father before her could have only dreamed of at her age. Perhaps Stable 83 could have been a truly wonderful place to live one day, had it not been destroyed.

Winterwillow had only just been made the official Overseer two weeks prior when the stable's alarm system went off, alerting to a breach of the main door. Buttermilk was with her in the Overseer's office when the alarms were triggered. Unbeknownst to her, he had been trained in how to protect the Overseer in case of emergency. He ushered her through a secret escape tunnel until they emerged into the cellar of a pre-war surface home. They remained in this safe house for four days before they returned to the stable.

Their home had been destroyed. Most of the residents were missing; the only ones that were left behind were dead. Winter knew someone from the surface world must have taken them, but she couldn't know where. After gathering what supplies they could, her and Buttermilk left the stable behind in search of the missing residents. She was their leader, and it was her duty to save them. Even if she had to travel the entire world, Winterwillow vowed that she would save every deer or pony from Stable 83 that she could possibly could, and together, they would find a new home.