I like the look of that American Girl book. DD has their puberty book and it's excellent. I like Markham pretty well, but the reviews of that book indicate it's similar to Siblings without Rivalry, which I have read and reread! We can use that S w/o R approach decently for actual conflicts over real things, like "You want to go to the library and you want to go swimming," and it is relatively productive. But that's really not what our main issue is here. It's deeper and harder to get a hold of.