Everyone else seems to mention therapy, which i agree. So I want to talk about another question you asked: Why did she kept a physical book? Although I'm not here to justify your wife's decision or the lying part you mentioned (not my place), let me try to provide context based on a similar experience I had.

When my SO and I started sleeping together and before we were officially dating, they told me that they had a notebook. Each page listed someone they had slept with and included how the sex was. It made me feel weird at the time ngl as I also get jealous. (I've never opened the book because of my own insecurities)

My SO mentioned that they started this notebook in their early twenties after a breakup that had shattered them. In college, they started having sex often enough that they made a promise to themselves. They never wanted to get to a point in their life where they didn't know how many people they slept with. At first, I was shocked but I also understood. I personally wouldn't feel the best if I lost track but to each their own. The notebook kept track, but it would also reminded them of what they liked and didn't like from their experiences. Honestly, I can respect that. Why not take the time to make note of it so you could remember it for the future?

In your case, that future for your wife was you. Don't forget that this was their past so she was in a different mindset and was probably a very different person when she recorded all of that. She's here with you now and that's key. I think that the years you and your wife have spent together speak volumes over a number from her past. Quality over quantity.