I assumed that this word "nun" popping up and replacing other words was some sort of joke that I was unaware of, but if so, I guess I'm not the only one who's clueless.
I don't think I'd go so far as to rank marriage among distant relatives up there with child labor, slavery, and the like. How distant is OK? Apparently, most European royalty is related to each other and marriage partners come from other royal families who are related. (And I discovered that my nephew and his girl friend, who met at college in a large city, are fourth cousins ... you never know what you'll find when you have a genealogist in the family!)
We've been told that marriage between first cousins became outlawed, presumably in the 20th century, because of advances in understanding genetics -- in other words, because of science, not moral or ethical reasons. However, I recently saw an article that said there actually is no reason, genetically speaking, that first cousins can't marry, because the genetic distance is great enough that fears that their offspring would have two heads, etc., is unfounded. I suspect that marriage between cousins simply seems uncomfortable to us because that is a 20th century view.
But to return to this as subject matter for Lara Parker's new novel, I would have to say it's not what I would be interested in reading.