Kinda but not really spoiler but just my opinion [spoiler] Dude just declare Marie the lost princess. She clearly knows a ton of stuff that makes her "worthy", and if someone else claims to be the lost princess than you found her!!! And you can proclaim her a fake and marry Marie anyway.
[spoiler] Marie is seriously carrying this girl. I mean what will she do without Marie if she is chosen??? I mean come on. At this point we all can see what this is leading to.
Does she legit think that will work? [spoiler] I mean based on physical position alone how the heck is MC supposed to have stabbed her? Plus the timing is to convenient. AND MC outranks her, so in a she said/she said usually rank prevails???