Sabrina went through "character inflation" pretty fast - from high school teen to queen of hell. Where else can they go with it?
This is a common failing with fantasy and sci-fi series. Your hero has to overcome the big bad in one season or movie. So they have to come up with a bigger bad to hold the audiences interest. For example, who would care about Superman stopping some bank robbers? You know he will win so there is no drama. So they have to come up with Lex Luthor or General Zod, who have a chance to win.