I think the game is a lot simpler than many people on the official forums make it. One of the marketing blurbs calls it "A game of growing up." On the page with the portraits of the girls, there's a picture frame filled with static with the legend "For when you've learned your lesson."
In Tarot, Death represents change, development, and transition. I believe it serves the same purpose here. Each of the girls dies and is buried in the old cemetery. Each of the girls is also a certain phase in growing up. The deaths represent permanently leaving behind a defining feature; something that made each of the girls what they are, and something they can never fully return to. Whether they're all the same girl or different girls doesn't really matter.
Robin: Her world is one of curiosity, exploration, and play; centered upon herself -- the never-ending golden summers at grandmother's house; the world is exciting and scary but she's also protected and sheltered by others; it only seems scary but isn't really. Her wolf represents the moment she becomes aware of her own mortality: people die and get put into the ground, and that will happen to her as well. That makes it possible for her to develop empathy for other creatures; use her imagination to make things better for others.
Rose: She is all empathy. In a way, she's a naive version of the Buddhist aspiration in the thread I started on P&R -- she cares deeply about all living things, and wants to make things better for them. In fact, she *does* make it better for them, in her imagination; her bunny is, for her, the world and everything in it. Her wolf is the moment she experiences the difference between dreams and hard reality; that simply wishing and imagining for something to be better won't make it so. She has to give up her mist and fantasy and return to the real world.
Ginger: She's all empiricism and experience: inquisitive about the world, oriented outward to it, absorbing things about it and rearranging them in her mind. Her wolf is her sexual awakening -- the realization that she's home to feelings and impulses that are, at least in the beginning, beyond her control. The Girl in Red plays with her, and then transforms the play into seduction. Her color -- red -- is a pretty clear connection to menstruation. That's what Ginger will have to confront and overcome in order to continue her growth.
Ruby: Rebellion. She rejects the norms forced on her by her (invisible) parents and (visible) siblings; she's lost, searching for herself, and defending herself by withdrawing into a hostile shell, rejecting anyone who approaches her -- "Whatever it is you want, I probably don't have it." She has to let down those defenses and let someone in, to understand that she won't lose herself even if she does that.
Carmen: Dependence. She's the mirror image of Ruby: where Ruby rejects anyone approaching her, Carmen thrives on the effect she has on others. She treats her sexuality as a plaything and an instrument of power; she's discovered what she can do with it, both for herself and to manipulate others. She has to discover that there's more to it than that, that sex and sexuality are deep and powerful; that they have the capability to wound and heal -- that they're more like the fire she plays with in the woodcutter's camp than the warm and wet water she enjoys in the bath. The homely, older woodcutter was comfortable with his sexuality, and the tricks Carmen had learned to manipulate men didn't affect him. They just sat by the fire and shared a beer. I took the rather powerful and disturbing Carmen's House to mean that, completely against her wishes, intentions, and plans, *she* fell for *him* -- the sexual power she had been using on others turned right back and bit her, and what was in the House was an unfulfilled and guilty fantasy of hers.
Scarlet: Responsibility and self-effacement. She sees herself as sacrificing her own well-being for others, and consequently feel superior -- morally, aesthetically, intellectually. She doesn't seem like a very fun kind of person to be around; she's continuously looking down on others while feeling that she sacrifices herself for them. She has to learn that, ultimately, everyone is responsible for their own well-being; the other girls she cares for on the one hand, and she, herself, on the other. When she meets her wolf, she realizes, perhaps, that she's not quite as superior as she thinks she is, and will consequently be able to interact with others as an equal, rather than as the superior/martyr she imagines herself.
Girl in White: Adulthood. She protects and guides each of the red girls through the game, and in the Epilogue, she cuts open the false grandmother, letting each of the girls climb out of her belly (the door in the starting room) -- each of the girls is reborn as facets of a balanced, complete, adult personality. They can even go back to being themselves, revisit things left unresolved, or favorite places, but they're now transformed by the experience into something other than they were before it.