I understand her wanting one of her daughters to be the one to marry the prince, and it was obvious that it was for her own purposes, not because she wanted them to live happily ever after. Basically, she wanted to become royalty and gain some popwer, and return to the life of luxury she had with Cinerella's father.

This being said, once she figured out that Cinderella was the the mystery girl who danced with the prince, rather than locking her up in the tower, wouldn't it have been in her best interests to try some last minute reconsiliation and sucking up to her in a last ditch effort to get into her good graces?

By then, it was pretty obvious that her daughters werent going to be the one, so shouldn't she have wanted Cinderella to become the princess rather than nobody in her family? As awful as they were to her, Cinderella always seemed to treat them like her family, and lets face it, they were the closest thing to family she had. The Step Mom really dropped the ball on that one.

I know in the Grimm telling, the step sisters try to suck up to Cinderella when she becomes princess and get their eyes pecked out by birds, but this is Disney and the step family flat out mussed an oportunity.