She's the daughter of the current king's guards/knights. They were both guarding him and are, from context clues of the story, presumably gone now.
The family opposes his rule, it isn't stated why as of yet. It's his father's brother who is the opposition, his uncle. They call him "former king's brother" and he refers to him as uncle a few times when thinking to himself.
It's all rather confusing. That's established so far. From here on is my guess of how things will go. Her family (Frim/MC) is opposed to the current king's rule because they blame the deaths of her parents on him for some reason. They are now going to harass her over picking the "enemy's" side now.
Is she the daughter of the kings brother or smth?