I understand her hesitation to kill someone, but the smart move was to off Yuriel right here. From a pure game mechanics perspective it would have taken them all back in time, and caused different, perhaps more favourable choices to come about. The clearest route for the Princess's victory, in my eyes, is to play Sans from Undertale. By making the game brutally difficult and causing constant game overs when the player tries advance the story, the player may give up and settle for peacefully leaving with a single male lead. Of course, that involves ruthlessly killing Yuriel repeatedly, and I respect the her desire not to.