Even if the sister where to have good intentions, this isn't one of the case where the end justify the means.
In particular I see many issues on how sister plans where made with no concerns of other people, putting them at risk just for "proving a point" and splitting these 2 and re-isolate her. Not only that, these plans practically risked to expose the existence of Wolf people, and animal people at large, to humans that don't know they exists.
In this last instance she also self-doxxed her own HOME (and his home too).
Tengu girl was also self destructing, I cannot imagine her tengu family would be happy of having a scoop exposing demihumans.
She may want to prevent her sister to become stuck like the father, and maybe she thinks it's an exposure risk if they are together, but she is doing that in a way that's certain to destroy her semi-normal life, that is what the father mostly want to avoid, he is afraid that by allowing the relationship to continue she would end up stuck in wolf form and not being able to have a normal life.
