Why did Crielle decide to send Efnisien to Hillview instead of disposing of him herself? If you’re at liberty to say, that is.
There's actually a few different things going on re: Hillview vs. killing him herself, and they are:
From a scientific viewpoint, Crielle is distantly curious to see if Hillview can actually rehabilitate or change any of her 'science.'
If it ever gets leaked that she had an omega in the family, it will be expected that she at least try to send him to a rehabilitation centre before killing him, because it's considered disreputable to not even try, when you have the money to spend on the matter. And Crielle cares a lot about reputation.
I do think it's genuinely hard for Crielle to kill Efnisien, not because she cares about him, but because she isn't ready to completely eliminate a science project that she sunk almost two decades of her life into. Sometimes authors shelve a book they know will never be published because it's bad, but they can't bring themselves to delete it, so they put it away so it's 'there but forgotten.' I think Crielle has done this emotional equivalent with Efnisien. But much in the same way that a book is an object, she views Efnisien as an object too.
So yeah, there's definitely a few things going on!
That doesn't mean that Efnisien's life isn't in danger re: Crielle, because it still very much is. But for now, Efnisien is the metaphorical book shoved into a folder to be forgotten about.