**spoiler**
She definitely is the duke’s daughters. The king entrusted the shitty parents with her. The king is also behind the dukes missing wife and daughter. Her eye colour and the duchess’s eye colour is the same. There is a bit of conflict as to why the king doesn’t know about pink or red eyes. But he was withholding an artifact that could help the duke find his daughter but only gave it up just when the ‘daughter with pink eyes’ showed up (that was sent by the emperor himself). So it’s possible the artifact itself is tempered with. That also shows his hand in this matter and the fact that he used a spell that could kill the shitty dad if he ever utters the truth shows it’s regarding someone that could even threaten the emperor’s position.
It’s either that or the duke himself used a powerful spell to distort memory of the people who met her into believing her eyes were pink just to ensure there are no fakes or that the baby never actually had her mother eyes. Going by the last 2 chapters it’s also possible that the fl has her grandmothers eyes. The head maid’s reaction and the fact that the grandmothers face was shown is a testament to that.
I’m up to chapter 21, is that black haired dude fl’s dad or something? Are the bastards not her actual parents???