User blog comment:Zathronas/Speculative author: Family Tree part 2/@comment-5217560-20140908002336

Regarding your Yang and Cinder being sisters, Monty diiid say that a child's semblance can share traits of the parent's semblance, so both having a relation to fiire....

Although Cinder having flame based abilities could be just be due to Dust and not her actual Semblance.

Your theory is basically what happened with Cora and her two daughters in Once Upon a Time. In order to achieve a higher social status, Cora gave up her first Born, Zelena. Then when she married into royalty, she had Regina. Zelena grew up depraved of care and luxury so when she found out about Regina, she became incredibly jealous and tried to undo everything by going back in time and changing the one event that messed up Zelena's life.

While that would be a cool take in the RWBY world, I just don't think that is Cinder's reason for being. It's too....petty for her. To small a reason I believe for her wanting to do whatever it is that she is trying to do. She seems so much more complex than that. And she looks pretty well off I might add.