@marrow
Pettier than Mielle ? Pettier than the girl who made the servants bully Aria, poisoned her mother and made her executed before Aria came back in time? Even since she came back she tried to kill her once with the carriage.
And what Aria is doing now is trying to make the engagement between Oskar and Mielle break hoping it will help her not being executed this time which is understandable. She said that she was hoping that they Mielle would end up executed in the end but I think it's pretty understandable too when that said person tricked you in being executed before.
And the little tricks she does before using the hourglass doesn't hurt anyone in the end since they didn't even know it happened. And I can understand why Aria take pleasure in doing that to the person who ruined her previous life.