I'm gonna bet on the confusing a king for her on the fact of tsunderes being crazy jealous and what not. By the way, I have no clue about her real personality, I'm just assuming out the wazoo.
From the bio on her for Fate/Apocrypha hints towards her personality:
"She is taciturn and cool when acting as a Servant, but her natural self is a plain and quiet sixteen-year-old girl. She puts order first, and will wield a sword for the sake of the rules, but fundamentally believes "all people and Heroic Spirits participating in the Holy Grail War are important."
CoCoMoo said: From the bio on her for Fate/Apocrypha hints towards her personality:
"She is taciturn and cool when acting as a Servant, but her natural self is a plain and quiet sixteen-year-old girl. She puts order first, and will wield a sword for the sake of the rules, but fundamentally believes "all people and Heroic Spirits participating in the Holy Grail War are important."
However, Jeanne and Gils were allies and friends. So her being mad at him for what he's done after they parted... yeah.