Wll, I want to say

BPD is a conundrum of an illness. Just so many behaviors that just seem confusing and self destructive and unsolvable. I know how you feel right now. Dealing with a pwBPD sucks out your energy.
Regarding the notebook - so weird. Do you think she threw it away intentionally? Possibly it was an accident, but when dealing with a pwBPD - there is a chance she intentionally threw it away. My significant other tends to hate clutter, and will tend to go through phases where she wants to throw out everything, often focusing on MY things. And she will throw away things that are important - bills, instructions, clothes... . I wouldn't put it past her to get rid of something of mine if she was mad at me and found a way to resent it. I did have a previous BPD/NPD partner who went through my cabinets the first time she came to my house, throwing away things that I later found in the trash. She somehow thought she was doing me a favor, helping me "better" myself and organize my life. Umm. One of the things she threw away was my toothpaste. Apparently she thought I was using the wrong brand. So maybe that is the case with your notebook? Have you asked her about it?