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Vahneris: Nope, doesn't feel like the Princess "SACRIFICE" part is the reason for what he did. He is just seems like the yandere/possessive type who can't accept anyone getting closer to the person they like.
If he wanted to really stop the Princess from sacrificing herself, then he would have worked anyway possible to help her while also saving her, which also means working with Red.
Also the Sacrifice part isn't really related to the current situation, but rather the whole situation with those Magic Seeds. So, sabotaging Red here doesn't really help or gain anything nor does it stop what the Princess wants to do.
Most likely, the Author wants Rosie to go rouge and become something equivalent to the Anti-Hero Ranger's (like Green Ranger, White Dino Ranger, etc), or something like Icelander/Yllbora Saro from an old anime called "Ninja Robots/Ninja Senshi Tobikage".