At some point, every conceivable fan-fictiony alternative point of view in classic fiction will have been used. There's the story of the girls' father in March; coincidentally there is the story of Huck's father in (also coincidentally) Finn. And of course there's Wicked. And so on. Jacob T. Marley belongs to this family, spinning Dickens's A Christmas Carol to explore the story of Scrooge's partner. How does a man come to be a spirit weighted down with chains and money boxes, wailing in the dark? Here Marley's past is postulated, a past that makes him almost worse than Scrooge (or gives him less of an excuse, in a way). In A Christmas Carol Marley is unredeemed, perhaps unredeemable; here that is rectified.
I'm not entirely sure the writing is successful as an echo of Dickens. For one example, I could well be wrong, but such open discussion of pregnancy was impossible in 1843… The language is enjoyable, but is not Dickens; of course, it doesn't need to be, and hopefully was not trying to be. I'm not entirely sure it was necessary to tell Marley's story; I'm not entirely sure much was added to the original. But it is well-told, and is overall lovely.