This is my opinion only. But I believe the reasons that Evil Queen from Snow White and Lady Treamine from Aschenputtel mistreat the titular characters is different from the in-story explanation.

Evil Queen used the fact Snow was pretty as an excuse to get rid of an heir to the thron which I presumable that the Queen was ruling for Snow.

Lady Treamine's daughters might be older Von a few months in the animated Disney movie. And back in those days older daughters were suppose to marry before younger ones.

I don't really have a reason for Edward's step-mother, Narcissa. But I assume that the Kingdom is suppose to be run mostly Von a Queen?