@Iheart
Yes, its an understandable reason, to a degree. But that doesn't make her actions any better, nor her extremely skewed judgement.
Like Drake said in this Chapter, a soldiers purpose is to follow Orders, not chase Vengeance in War. Fighting exclusively for Vengeance
never leads to anything good in the long run.
Legadonia started the War, and Marys Father had numerous opportonities to turn away and return to his family instead of continuing to fight. He chose to fight anyway and died. Thats sad, and its understandable that Mary would be angry about it, but her single-minded focus on Vengeance above anything else will only lead to more suffering in the end, not less.