I think a more useful novel to compare it to would be Toni Morrison's Beloved. They're both novels about slavery in the American South, written in the third person but focused on the point of view of the slaves - specifically, enslaved women, enslaved mothers. They're both written by women who were personally descended from slaves, but who were not born until several generations after slavery ended. They're also both based on specific real-life people. But the real-life people chosen are a bit different, in ways that deeply affect the books.
Toni Morrison based Beloved on a real-life story she found in history records, that she was inspired to write about precisely because it was unusually horrific - the story of a woman who killed her own children in order to spare them from being made slaves, because her whole family was about to be recaptured. Margaret Walker based Jubilee on a real-life story that she was inspired to write about in large part because her own great-grandmother was the person whose story it was. The result is that although Beloved tells a story a little more horrific, the reader can read it with a certain comforting thought in the back of their mind that, after all, this wasn't exactly the average slave's experience; this was an exceptionally bad experience, not completely entirely exceptional of course, but you know, at least a little exceptional. With Jubilee, that reassurance is not available. Margaret Walker is not writing this story because it's exceptional in any way; rather, she's writing it largely because it's so typical.
I think Jubilee benefits humongously from Margaret Walker's determination to stick exactly to the truth. On every other page I kept envisioning ways that a typical fiction writer would be highly unlikely to resist either ridiculously romanticizing the story and tacking on an unrealistically neat happy ending ("But even though she hadn't heard from him in seven years, she was determined to still remain faithful to him, until one day slavery was abolished and he showed up again and it turned out he'd remained just as faithful to her for the whole seven years, so they promptly re-formed a conventional nuclear family and lived happily ever after"), or filling it with unnecessary melodrama and soap-opera-ishness ("Then after she'd remarried a different man, her original husband abruptly showed up and announced he wanted her back, so they decided to fight a duel to the death over her on the front lawn"). At some points, I really began to doubt that it was possible to end this story in any way that would manage to remain completely credible and un-trite. But in the end, absolutely she managed it. I'm not sure I've ever seen an author write an ending this completely true-feeling who wasn't basing their fiction on a real-life story.
Jubilee also differs from Beloved stylistically, in terms of its use of language and the structure of its narration. Beloved is a vastly more modern (postmodern?) book, and comes with all the trendy turn-of-the-millennium experimentalism that readers of contemporary classics-to-be have come to expect. Jubilee is copyright 1966, and stylistically it reads more like a classic 19th century novel than a 20th century one, let alone a 21st century one like Beloved verges on being. Aside from a bit of an effort to convey the slaves' accents, the book is as stylistically conventional as you're ever likely to find - well, aside from that and the fact that it tells such an unromanticized truth, which really is the most profoundly unconventional thing any writer can ever do. I think the conventional trappings of the story work really well for it, because the unadorned truth of the story is what the reader needs to remain focused on, and excessive wordplay that called attention to itself would have distracted from that focus.
I know I'm telling you very little about what actually happened in the book. Often when I write about novels I do feel free to reveal pretty much the whole story, because it seems like for most novels I read, an element of surprise is really not in the least necessary. To some extent it's not necessary for Jubilee either; this is not a suspense novel, and if you did know the entire story before you read it, you'd probably get about 95% as much the same experience as if you didn't. Still, the stylistically conventional storytelling structure makes me feel that I should adhere more strictly than usual to conventional rules about how a reader should never know the end until they get there. So the only things I will tell you about the plot are these:
Vyry is a woman born into slavery, whose mother was a slave and whose father was the man who "owned" her mother. (If the novel has a fault, I think it is that Vyry's mother's probable resentment of being raped by the master is not portrayed. The novel certainly doesn't claim she didn't resent it, but it doesn't say much at all about what her feelings were about it, and I wish the author could have found a way to say at least a little about something so important.) Vyry's mother dies in childbirth, not while giving birth to Vyry, but while giving birth to a later child, born dead, while Vyry is still so young that she grows up unable to remember her mother at all. Vyry is so pale-skinned, and so eerily similar to the master's white daughter, that she's extremely frequently mistaken for white, frequently mistaken for her white half-sister, and easily recognized by all who meet her as being her father's daughter. And the master's wife, jealous and bitter over the master's infidelity, hates Vyry for the family resemblance. But that's all I'm going to tell you about that - all of which is revealed within the first 20 pages or so.
Actually, there's one scene in the book that I wanted to ask for some help making sense of, that might be a bigger fault. At one point, Vyry abruptly unbuttons her dress to reveal - to her husband whom she's already had two children by, and whose third child she's currently pregnant with - that she was badly scarred by a whipping when she attempted to escape from slavery and was caught. The author says very clearly that her husband had been unaware until then that Vyry had ever been whipped. The author also says very clearly that the scars are quite severe, all over her back, plus a loose flap of flesh over one breast that had been partly torn off and left to heal at the wrong angle. Now, it may just be that I'm underestimating the extremes of Victorian prudishness that led married couples to never ever ever ever see each other naked, and not even to feel around enough to discover severe scarring before being about to have their third child together . . . but I'm having a really hard time getting my mind around it. Then again, I'm also having a really hard time getting my mind around how an author who wrote every single other page of the book so beautifully could possibly have just accidentally overlooked a detail as glaring as that. Is it possible after all? Someone, help me make sense of it!
Regardless, you should all read this book. No matter what is or isn't wrong with that scene, the book as a whole is brilliant and amazing.