The feminist criticism of this version of the story feels like reaching to me. I saw it as a story about a character whose inherent goodness is constantly pushed and tested but who stays firm in her convictions (yeah yeah, courage and kindness) and displays tremendous strength and optimism in the face of constant, unwavering abuse. And she was always able to see past her own miserable situation to look out for those around her, too. That's not a weak character to me.
It's not like she was waiting around hoping for the prince to come rescue her, either. Hell, even when she desperately wanted to go out to the ball and see him, she had no clue he was a prince, or even a potential husband, really. She just wanted a brief escape from that awful home life for a social engagement with someone she met and connected with once. Basically, the girl just wanted a night out for some socializing, lol.
And yes, she is ultimately "rescued" from that life by marrying the king, but that happened to her directly because of who she was and her strength of spirit. I thought it was a really nice touch how the prince took on her mantra/philosophy as his own, subsequently convincing his father that he was finally fit to run his own kingdom (and life), thus compelling his father to give his blessing to marry for love. I think the main message young people would get from this film is that if you are a relentlessly good person then good things can happen to you. And I don't think that's a terrible message to send out at all.
It kind of bothers me that the only strong female characters that get praised in movies are the "ass-kicking" types, like the Ever After version of this character (which I also love) who fights back at every opportunity. For some people trapped or born into horrible circumstances, "fighting back" in the traditional sense is not a realistic option. THIS version of Cinderella displayed a much more subtle kind of strength - the ability to make the best of the situation she's been dealt, with pure resilience, courage, kindness and optimism, always looking for ways to improve it. She's able to find her own happiness while trapped in a circumstance in which many of us could not. I don't see how that makes for a bad role model.