Yes, you see, the reason that she was tortured is because, honestly, her sister hated her. Something to explain:
back in the empire, there was a time the aristocracy had way more power over commoners and such and were abusive. But a silver haired and multicolored eyed man basically destroyed that so there's a stigma against those with one or more of those traits if born in nobility. She was born a Duke's daughter, but hated just cause of how she looked. So her younger sister tormented her and basically abused her. Crying, she was seen by the prince, the prince was charmed by her and asked his father to make her his fiance, see the royalty liked the hero of the past too cause it basically helped the royalty regain some control from the aristocracy too and they found her to be a good girl.
So, years pass, her sister basically slowly poisoned the prince's mind and the day of their wedding (which was literally the day or so after they banged) the prince broke the engagement for "crimes against abusing her younger sister" (remember, the younger sister was basically sleeping with the prince, and others, and lying about what she had been through). She was tortured to force her crime, she never did, escaped after a month of torture. Sadly, the emperor, the empress, and the princess (who loves our MC like an older sister) were away on a tour, when they got back, they were quite pissed, but eventually, the crown prince and his faction had them assassinated (the emperor and empress) and the prince became the emperor with our MC's sister as empress.
Anyways, years and years pass, they don't even think she was alive anymore, but find out later and, because the empress (MC's sister) was such a slut, she had gotten STDs that made her infertile. To secure her position, the emperor thought to get "his" daughters back and make them inheritors to the throne to settle that issue. That's when we'll see them come into the story later.
To give more spoilers, it doesn't go well with them. There's a challenge battle at a coliseum basically to decide between the empire and kingdom that our MC is in right now who gets the kids and other things and the MC is just way too broken. Also, the moment everyone sees her again for the first time is amusing because she hasn't aged a day and is still beautiful and that makes the emperor have some regrets and her sister stupid jealous.