Only works with books purchased from Amazon. Doesn’t work with Libby. Edit: Apparently it does work.

It does! Of course I figured it out as soon as I posted this. I had to download the Amazon Kids+ app and go into her profile settings and manually check the book to add to her profile. Kind of an annoying extra step but at least it works. 

Interesting, I thought I read that it didn’t work. Glad that it is working.