We all have different tastes in reading and ice cream, for sure, but I would like to respectfully disagree with the idea that the author was trying to "rewrite" a fairy tale, that she made it up as she went along, or got lazy at the ending. Marisa Silver shows us at the level of her sentences that she's a very purposeful and accomplished writer.
I've read a lot of fantasy, magic realism and science fiction, so I did not expect everything to make literal sense in the ways of our physical world. Fairy tales work the same way this book does -- things happen that we know could never happen in reality. We don't expect them to make sense. Silver used magical transformations in this book the same way that we see them used in fairy tales, but she also made the characters "real" people, unlike the figures in fairy tales. The main characters are not all good or all evil, and we see their struggles from within. She gives us enough understanding of them to care about them way more than we would care about Cinderella or Jack in the Beanstalk. And she puts them into a world that is very much like our own, in history, but also relevant to today. She does that for a reason beyond entertaining us. She isn't trying to "rewrite" any particular fairy tale, but to borrow the magic of fairy tales to tell a purposeful story of her own. The author uses the magic of fairy tales to address the powers of goodness and evil in our human souls (which is true to the origins of fairy tales as well, though not the Disney versions).
Pavla's transformations aren't sloppy storytelling, they are central to this novel, and meaningful, but symbolic. When people are treated as less than human, and abused (even "for their own good"), for their physical differences -- they can be reduced to the appearance of being animals in the eyes of society, and sometimes even act that way. That's Pavla being turned into a wolf. What "brings her back" to her humanity is her love for her dying parents.... When we experience the kind of trauma Pavla did, we can respond as she does initially, withdrawing, disassociating, reducing our minds to simple survival mode-- but also, moved by love, we can find within ourselves the strength of choosing to "rise above it all." That's Pavla as a prisoner, forgiving, caring for others, valuing the gift of her soul, being grateful for life itself. (And again, that happens after she sees Danilo and Markus in the prison. She's reawakened through love.)
The author took a risk, it is harder to switch back and forth between the symbolism and magic of fairy tales to the world of real people, and no one has to like it, but just because we don't like something, doesn't mean it was a failure of the author. I was challenged, but I am glad I read this book.