You'll find everything out as the story progresses, in the manhwa we have learned that Yvonne isn't really herself or 'human' anymore and it has a lot to do with the evil wizards (Leila). In this chapter you can tell she mostly wants to control the kingdom, she brainwashed Eclis to become the ruler.
Oooh thanks ! Leila ?? Is that a character we have already seen ?
So the current yvonne is yvonnes body but she is being controlled somehow ?
Yeah at the beginning I thought she just wanted to regain her position but when I saw what she did to Eclis, i didnt understand like why did she want to conquer the empire ? Now its clearer

i don't really remember that manhwa, do we know yvonne's goal ? Like why kill the crown prince ? Does she want to regain her place as the only dukes daughter ?
I do remember she is some weird a** sorcerer and that she hypnotized her big brother during penelope birthday.