Based on the small tidbits hinted throughout the story I would not be surprised if she was related to a royal like that. Or perhaps her mom was a queen who had her out of wedlock, but the latest chapter suggests she came from a family of power and the war literally started because of her.
Whether it was for her hand in marriage to warring princes or her legitimacy as an heir has yet to be resolved. There is the possibility that her dad started the war because she mentions her mother and brother passing, but not him.

This may be a delusion of mine BUT…
I really hope that her back story is that she was a noble from a foreign country. Like her family was killed by evil relatives that took over the family and she had to run to escape but ended up captive in a different country and became a slave. In my delusion she’s the long lost daughter of a prominent family which would mean she’s not a commoner nor a slave.
Oh how sweet this would if it were true (╯°Д °)╯╧╧