First, there are a lot of bottle blondes out there. It might not be who you think it is at all. BUT, as you say, it's quite a coincidence for this book to arrive out of nowhere right after you saw her for lunch.
Second, are you sure your XH might not be involved with another woman? I thought mine couldn't because he had such problems with impotency due to his medications. Proved me wrong.
Third, could this 'friend' be involved, or perhaps wishes to be involved with your XH? I'm really sorry to say that, but that is sort of the scenario that got thrust on me when my H had his first A. It was with his best friends wife, and she became noticably upset when I talked to her about OUR R.
Just sayin'. Protect yourself GAG. No expectations. As far as this woman is concerned, don't trust her.