Personally I even fault MC for not controlling or checking on her more often.
is his mother, is brutal and ruthless and insane, made moreso from the collar he put on her.
And is a fact that if the collar was invisible she would have been able to keep some pride.
Note, she is evil from the first chapter that is true, but MC didn't do anything to keep her on the human sid,e if any he motvated her to go in this route.
She had everything in the world, is incredibly nacissistic and prideful to the point of tangible toxicity, humilitaing her like that would make go bad.
I like many parts of this story, but MC being so fucking lazy he lets problem he could kill in the buds grow is all on him (I know, the author had to make the plot exist).