Mike, ask politely for it once, tell her it's sentimental to you, if she refuses, let it go, it's just "stuff".
I agree with this. My theory is that our WAS are kind of doing stuff like this just to start trouble or fights and make it easier on themselves. My H is 10times more of a jerk maybe 100times more than he used to be. I also suspect that in a few months your W will realize she is being a jerk over the cookbook and if she won't return it now, if you don't make a big thing out of it hopefully in a few months your W will be more rational and agreeable at that point.
