It's a bit too on-the-nose, as if Campbell doesn't trust us to make the necessary connections, or perhaps didn't trust the ambiguity of her narrative. For all her tumult, after all, Margo is in the act of becoming, a child who grows into a woman as the book goes on. To see her at novel's end, "with her own safe and snug place on the river," is to recognize this, to see her at-times meandering saga as an extended slice-of-life. That's the key to Campbell's stories, which eschew easy summaries, easy conclusions, and are all the more astonishing for doing so.
That leaves us with a question about the relationship between novels and short fiction, about what they have in common and what they never will. Campbell is a brilliant story writer, but although there is much to admire in it, "Once Upon a River" lacks the intensity of her shorter work.
This is not a matter of focus; if anything, the novel is too focused, too overt. No, it's more that in the long form, Campbell seems not quite able to rely on her instincts when, as Margo knows, instinct is the only thing we've got.