The Schnee Dust Company is owned by Winter's family. It was founded by her grandfather and is currently run by her father. Winter herself does not work for the company, though she was present at the SDC World Headquarters the day Weiss called for information.
It is confirmed in "Punished" that Winter's title as heiress to her father's company was revoked upon her decision to join the military.
Winter is a member of the Atlesian Military. She is a member of the military's Special Operatives unit, and Qrow accordingly refers to her as a Specialist. She is also a subordinate of General Ironwood, whom she addresses as "sir".
Winter trained Weiss at least once prior to Weiss' fight against the Arma Gigas. She told her sister that she had to become stronger if she wanted to leave.
Although initially cold to Weiss, Winter has genuine concern for her sister's well-being, inquiring about her social life and eating habits, rather than just her studies and class rank. However, her methods of demonstrating this affection are rather unusual, rebuking her sister for misinterpreting her previously-mentioned inquiries and proceeding to slap her on the head for it.
She also knows of her sister neglecting their father, and can sympathize with the situation. She tells Weiss that if she wants to explore Remnant and learn about herself then she cannot answer to their father. She gives Weiss one last hug before departing.
After she and Weiss reunited in Atlas, she expressed relief to see Weiss again. As she continued to criticize Weiss for her actions and methods of re-entering Atlas, Weiss embraced her in a heartwarming hug before Winter hugs her back.
In "Sparks", she entrusts Weiss to keep her secret about her becoming a next host as the Winter Maiden after Fria passes away.
Not much is known about Winter's relationship with her father, but it is implied that at some point it was a strained one. The extent of this compared to her sister's is unknown. During her conversation with Weiss, she mentions how she had been financially cut off from their father as well, then recalls her amusement towards their father's reaction the day Weiss left for Beacon. It is also hinted that their father was not pleased with Winter's decision to join the Atlesian Military when she graduated from Atlas.
When Weiss admits that their father cut off her access to his credit card, Winter gives two options as advice. One is to call him, beg for his money back and try explaining once more why she chose to study at Beacon. Winter's tone of voice hints that the conversation would likely be heated and needless. The other option is for Weiss to continue as she has been, exploring Remnant and learning more about the world and herself. This option indicates that Winter is not opposed to Weiss being independent of their father.
Both Winter mentioning seeing their father's face the day Weiss left, and her awareness of Weiss' repeated attempts to explain why she wanted to go to Beacon indicate that Winter is still in communication with him. It remains unclear how frequently they communicate or how well they get along.
In "Pomp and Circumstance", she avoids seeing her father after Weiss confronted her father with her team.
In "Sparks", she is shock about her father shutting down all nonessential SDC operations in Mantle if he's not election as council and comments that their father has found a spark to set the Kingdom on fire.
Weiss has stated that her and her sister's younger brother dislikes Winter; however, Whitley claims to have a strong sense of respect for her.
Ironwood is Winter's superior in the Atlesian Military. As such, she has great respect for Ironwood and follows his every order almost without question. Ironwood appears to reciprocate this respect, as he considers Winter one of his best when arguing with her father.
Winter appears to be previously acquainted with Qrow, as she is on first name basis with him. They have a pre-existing enmity and seemingly very little mutual respect. Winter responds to his initial dialogue with hostility, while Qrow enjoys provoking and angering her. In "It's Brawl in the Family", this culminates a battle in the middle of Beacon Academy's courtyard.
After they reunited in Altas, their relationship is still same from before. She blames Qrow for getting her sister, Weiss arrested.
Winter appears to think little of Ruby upon initially meeting her, stating that she is "appropriately underwhelming". She is, however, thankful to Ruby for "taking an interest" in Weiss. In the conflict between Winter and Qrow, Ruby sides with her uncle.
Fria is the current Winter Maiden. When Beacon fell, Ironwood gave Winter a secret assignment: to be Fria's only caretaker until her passing. In "Sparks", Winter has a good relationship with Fria, as they are seen having a nice cup of tea. As such, Winter is the only person Fria's allowed to see, meaning that Winter will become her successor once Fria passes away one day.