I would maybe put it in the back, not part of the book but in the book at the end, and write on the back "From B." Then let the bride decide if she wants to keep it or if she wants to toss it.
Or save the pic for after the wedding and then give it to A.
I would not include it. I am sure A has pictures of B to remember the good times. This book is about the people at her shower. B will not be at her shower. A can look back at her own pictures of B and remember her any time she wants without putting her in a book that is about people there for her NOW.
I would be inclined to leave it out. Maybe if their friendship hadn't ended so recently, I would include it, but it doesn't sound like the wound has had much time to heal. If I were receiving such a gift, I wouldn't want to see a photo of a friend that I'd had a recent falling out with (especially over something like that).