This episode is a disgrace to the series.
first off, it completely flanderizes the characters, turns them into way bigger brats than they normally are. This is likely done so you don’t feel as bad for them when they’re killed off. That brings me to my more important point.
You have the protagonist of the series, our heroine who we’ve been following for an entire season, basically get murdered in her sleep. She doesn’t even get a fighting chance. This is right after the episode where she gets training too. Ok, she doesn’t literally “die”, but the effects are practically the same. Her life was removed from her. She was nothing but an empty husk subservient to the villain, forced to do things completely out of her control. All character development, everything she ever was, was just gone, and she would have stayed that way, had she not been bailed out at the last second by an old man. Mind control in general is probably the worst plot device in the history of fiction, just from a writing stand point, but here it’s done especially bad.