They don't know how to do Snow White
Yes, Kristen Stewart was an awful choice and personally, I think she is an awful actress. Most of the time, she's projecting like she needs someone to tell her what to do, what to think, what to feel. She's not innocent or competent. She's definitely not good enough to play a character as important and iconic as Snow White.
Personally, I don't think the writers knew what the hell they were doing the character. As a storyteller myself, there's no way I would ever put a sword in Snow White's hand and send her into a battle. That's not only stupid, given how little training she has, its also a betrayal of what Snow White represents. I understand that these filmmakers want to empower women. But, I don't think they should do so at the cost of storytelling. Snow White is empowering and an inspiration but not in the sense that modern feminists want.
In my book, Snow White is supposed to be so good and pure that she literally brings out the best in everyone and everything she comes in contact with. She should be presented as the exact opposite of the queen. She should be so good and benign that animals flock to her or follow her... like in the cartoon. BUT, she shouldn't come off as a total airhead like Kristen Stewart either. She should be played like Melanie in GWTW. In my eyes, she should have stayed in one castle and the wicked queen stay in the other castle while the Huntsman goes to kill her.