Interesting, I hadn't seen that. I've just had a quick skim of the opening for now, but I'll go back and read the full thing later. The structure in the novel is definitely derived from the short story, but the major difference is that they're more obviously discussing a narrative of past events rather than their current situation. (And the layout is different, indented and the speakers' names bolded, which is probably necessary given it's now an interruption to the narrative flow rather than an elaboration).

The other thing that's obviously changed are the character backgrounds, Diana's is better, everyone else's is worse, or at least more strained (I also suspect Diana is significantly younger in the novel than in the short story). And the way they bring in money, which only really comes in at the end of the novel, has been switched around. Catherine remains the writer and Diana is just starting on the stage, but Mary has no fortune and simply runs the household, or at least the bits of it Mrs Poole doesn't, Justine is the artist, and Beatrice brews drugs for the medical establishment. There are even changes in physical description, Diana is a redhead, not dark, for instance (and cuts off her curls the first chance she gets).