I spent part of the evening reading (most of) Coming Home, and I now that I have, I think I'd say that Helen's universe is an AU of Xanthe's--similar, but one in which the BDSM roles are more institutionalized and more rigid (as an example, in Xanthe's verse, there's not an immediate visible way to know if someone is a sub or a top). I think that the similarities between Helen's verse and Xanthe's verse are pretty strong, though--at least as close, if not closer, as Xanthe's is to canon.