The hidden message in the movie - step mom wasn't naturally evil

Nope. The message was right there on screen. Only the ignorant would not notice it or deny it when it's pointed out.

Maybe not jealousy but control. I have known a few people rather similar to the stepmother in real life, and with both of those it seems to be mostly a question of control, they are control freaks who want to have full control of everything in their lives.

Cinderella's existence alone would have undermined that control because her father might listen to her rather than to the stepmom if those two happened to think differently of something, and she also would always remind him of his first wife, a rival to the stepmom even if she was dead as long as he would keep on thinking of her, he might, for example, do something in the way the dead wife would have liked it instead of the way the new wife would have preferred as long as the dead wife was fresh in the husband's memories, and with her well loved daughter there she would remain so.

If the husband had not died the stepmom might have started a serious husband hunt for Ella sooner rather than later, anything to get her out of the house. Somebody not too rich or too powerful, just somebody who'd get her out of the way and out of her father's eyes so stepmom could get that all important full control of him, or at least have an easier time fighting for it.

Ella was also a practical rival to her, for the resources of the house. A new dress or whatever to her would be money the stepmom would not be able to use for her own and her daughters' expenses.

And after the father died Cinderella was a heir to her father's money and possessions, at least part of them, and now a husband to her might have totally decimated the stepmom's resources - it does not come up in the movie, but since the fantasy kingdom seems to exist in at most 19th century one might assume the inheritance laws might be similar to the real ones as they existed in several European countries.

Which means Cinderella would probably inherit at least something, maybe half, but possibly also everything, BUT be able to get control of her inheritance rather late, perhaps in her mid-20's or even a bit later, UNLESS she married. And if she did marry then the husband would be the one who'd have control of what she owned (even if it had not been the king...). As long as she remained unmarried and under the age of legal adulthood for single women the stepmom would be the one who had that control, as her guardian if not her legalized mother, and could use the resources in whatever way she wanted, presumably with the intention of using them to find suitable husbands to her daughters and squirrel the rest somewhere where Cinderella would not be able to get at it once she was old enough to start fighting for that control.

So now it was very important to the stepmother to make sure Cinderella would not meet any suitable husband candidates, or if she did they would not get interested because she seemed to be just a servant.

And with luck, if the stepmom would be able to break her spirit fully perhaps she could keep the problematic stepdaughter as an unpaid servant too cowed to ask what was legally hers for the rest of her life.

So I think the main drivers for stepmother's behavior were not jealousy or anything like it (although at least some jealousy no doubt existed) but rather the need for full control of everything in her life and simple plain greed.

*facepalm*

Tremaine is still young and beautiful and perhaps would get a third husband if her treatment of Ella didn't discourage potential marks unless the guy in question has no children from any previous relationships.

She was more like naturally greedy.