It’s just like a tradition in the family! The princess must not show that much skin, so she must abide by those rules. It’s like how Muslim women must wear a hijab.
It's probably also because of the injury the princess took? I remember in one of the chapters when she was bleeding on that stone thing and the commander went to find her, her wrist was bleeding or sumn.
Wait y’all I’m confused why doesn’t he let the fake princess wear anything short sleeved