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 is not working for the company, though she was present at SDC World Headquarters the day Weiss called for information.
It is confirmed in "Punished" that Winter's title as heiress to her family's company was abdicated upon her decision to join the Atlesian 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 an Atlas Specialist. She is also a subordinate of General Ironwood, whom she addresses as "sir".
Winter trained Weiss at least once prior to Weiss fighting the Armored Knight. She told her sister 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.
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.
Weiss has stated that their younger brother dislikes Winter; however, Whitley does appear 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 orders almost without question.
Winter appears to be previously acquainted with Qrow. They have a preexisting enmity and seemingly very little mutual respect. Winter responds to his initial dialogue with hostility, and Qrow enjoys provoking and angering her. In "It's Brawl in the Family", this culminates in a battle in the middle of Beacon Academy's courtyard.
Winter appears to think little of Ruby upon initially meeting her, saying 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.