Doesn't mean she'll actually sell more books as a result. She's a ghoul.
Actually, it pretty much ensures that she'll sell more books. There may be a few people that were planning on buying her book who will change their mind about it because of her recent behavior, but there are far more people out there who wouldn't have even thought about her book (or wouldn't have known she had a book coming out) who will now buy a copy because, "hey, it's a trainwreck."
Publicists and agents know how the market works, and I have no doubt they understand that negative attention is far better than no attention when it comes to marketing a book.
Not usually. It's a gamble. Controversy may sell something like the Fifty Shades books. But generally speaking, as several of my friends in publishing have found out, while people may pick up, flip through, or read bits of a controversial book, getting them to actually spend twenty bucks on a hardcover of it is unlikely. Or, if sales are initially brisk, the book may taper off quickly and it quickly ends up in the remainder pile. (I used to see this a lot when I was working in a bigbox bookstore myself.) This is especially the case when it is a less-popular public figure.
On the other hand, the Kardashians, Sarah Palin, and Adam Carolla are bestselling authors, so who knows what will happen with evil Joan's book?