The king revealing to Anastasia about how much she reminds him of his dead wife really shows that Anastasia can be just as good of a bride to the prince is she was able to be herself and not be forced to be like Cinderella. As well as show that Anastasia can have some real growth in her character.
At first, it seems contradictory that the king ordered his men to find The Girl Who Fits This Slipper in the first movie but is the one who points out the plan's flaws in this one. But then consider the fact that the night of the ball, the king was drunk off his rocker, in hysterics, and desperate for his son to get married and make some grandkids for him. His state of mind led him to twist his son's words into a court order, but he sobered up by the next day and could think his plan over on a rational level. And yet even when he admitted his own plan had its gaping holes, the prince still wanted to go through with it.
The king mentions Cinderella's shoe size is 4.5. In US measurements, this is often the second smallest size (in a range between 4 and 12), if they even stock size 4 at all. This makes sense given how both her stepsisters have feet far too large to fit it.
Take a look at the painting of the queen. Then look at the pocket picture that the King has. They look like Cinderella and Anastasia respectively. You could pass this off as the painting being a dramatization of the pocket one. But the pocket picture only appears after Lady Tremaine does her spell. It was as if the painting was a prediction that the Prince would marry Cinderella.
While it may seems to be an animation error at first, Lady Tremaine destroying Cinderella's dress with magic when she teleports her inside the cursed coach makes sense when you realize that she wants to destroy any hope and dream the girl has from her magical night in the first movie.
It's established early on that magic is blocked or deflected by metal, and Prince Charming uses this to reflect Lady Tremaine's final spell back at her during the climax. That might seem like a bit of an arbitrary cop-out, but it actually makes perfect sense: this is fairy magic, specifically, that we're talking about here, and one of the classic weaknesses of the Fair Folk is metal, specifically iron.
The "Sweet Nightingale" number in the original movie showed Anastasia to be terrible at playing the flute while Drizella was equally terrible at singing. This film gives Anastasia multiple solo numbers, and while her singing voice isn't perfect, it's far easier on the ears than her sister's. This seems ironic at first, but it subtly fits Tremaine's controlling personality perfectly. She doesn't care if Drizella and Anastasia do what they like or what they're good at, just what they're told, and she decided that Drizella should sing and Anastasia should play the flute, regardless of whether this actually fits with the girls' individual talents or not. She may not have literally enslaved her daughters as she had done to her stepdaughter, but in a different way, she was just as abusive towards her two biological daughters as she was with Cinderella.
When Cinderella is banished, she's put on a ship to be sent off to a distant land. Just think about that a moment, a young beautiful girl stuck on a ship full of rough sailors who probably don't see women for as long as a month at a time.
The thought of Anastasia having to live a lie for the rest of her life if her mother's plan had gone through. Especially if the second plan had worked, when she's disguised as Cinderella. If they ever consummated the marriage...that is in fact rape.
It was only Lady Tremaine's self-centeredness that saved Cinderella. She was mentally turning back the clock to the moment she remembered everything going wrong. If she had been even slightly less laser-focused on vengeance, she could have gone back a mere 24 hours further to the points most important to Cinderella's story. She could have intercepted the invitation and prevented Cinderella from ever learning about the ball; she could have allowed Cinderella to attend in her simpler gown (to keep Fairy Godmother from needing to interfere) and used magic to bewitch the Prince into falling for one of the girls. She could have gone back in time and killed Cinderella outright.
