This is the 12679th most frequent Russian word.
королевой
"Королевой" is the instrumental singular form of "королева," meaning "queen" in English.
In this sentence, 'королевой' is the instrumental case of 'королева' used to denote 'being the queen of (the ball)'.
Она была королевой бала.
She was the queen of the ball.
Here, 'королевой' is the instrumental case used as part of the predicate to express pride towards 'queen'.
Я горжусь королевой своей страны.
I am proud of the queen of my country.
In this sentence, 'королевой' is the instrumental case indicating the role or status under which the action is performed (working as a queen).