User blog comment:Zathronas/Analysis by an author: Volume 2 episode 3/@comment-1618120-20140808094016/@comment-96.254.157.84-20140808125029

They are basing that since Weiss is the heir to the SDC that she is the next in line to take the company, meaning either Winter is her twin sister who was born shortly after or she is younger by a few years.