What do you think she did wrong? I read your amusing description of your family and I get the feeling you are trying to teach/correct her, and when she rebukes you or laughs it off, it upsets you. I'm curious to see what she did that would warrant an apology like that.
Sera gets pissy and continues to give evasive, nonsense answered even after you tell her to make sense. She KNOWS allies are important yet gets so mad she leaves when you ally with that noble. She knows you are a mage (if you play one) she agreed to join in the first place yet, has the gall to tell you to stop using magic. Tell her it isn't that simple, she insists that it is, despite evidence to the contrary.
Uneducated, naive is one thing, stupidity and, ignorance because you refuse to see any side except your own and, refuse to learn anything even when you have the opportunity is quite another. It shows a lack of awareness, lack of concern, lack of intelligence and, lack of any desire to better ones self. That's how Sera comes off to me.
Were she to say "Oh why isn't it that simple?" and allow Quizzy to explain a bit of politics and war to her, that would be different. If she would refuse to join a mage inquisitor, fine, she is terrified of magic and won't be around it. If she asked why you allied the noble then, let you explain why allies in high places are important, good but, she does none of those things. She does not want to learn, to better herself or to even understand anything. She has decided it's all about beat down, stupid, arrow in the face, dangle bags and mustaches and if it isn't as simple as saying "Stop being stupid" it is stupid. She chooses to remain uneducated, unaware and, to keep her ridiculous lack of consideration and understanding - she chooses to be a shallow minded, short sighted, selfish chit even when given the opportunity to become better educated, more aware, more informed, a better person.
Same as my idiot step relatives that can't even learn to say "Thank you." after being banned form my home by both myself and their father for their rudeness and refusal to think of us anything but money bags. They refuse to learn, to try to be decent people. I don't need them in my life, or in my game.
Not one of the companions is perfect but, at least the others try and, apologize when they realize they are wrong. Sera doesn't even try.