Is it a rule that since this is Rose’s blog, you shouldn’t discuss other cooks
More of a loose guideline. It is Rose’s blog and forum, and all of her recipes are welcomed for Show & Tell, Q&A, etc. On occasion, we venture into other authors/recipes (including our own), especially if it is for something that Rose hasn’t published a recipe for (like macarons or flour/milk-based frosting). Rose herself reviews and recommends other authors’ books/recipes, so it doesn’t seem like we need to keep strict limits on posting about non-Rose stuff. But for the most part that is the exception, rather than the rule.
As Woody points out, over on the blog it is best to limit questions to Rose’s recipes, as they cannot spare the time involved to try to trouble-shoot other authors’ recipes. If they started doing that, we’d have to wait ten years between books, instead of five!