Hi Why123,
Welcome to the BPD Family
I'm here because of my SO's (significant other's) uBPDxw (undiagnosed BPD ex-wife) so I come at this from a slightly different angle, but totally understand how complicated it can be to have someone with BPD in your life (everyone here "gets it"
When I first discovered BPD I hit the library and read everything I could on BPD... .it sounds like you are reading "Stop Walking on Eggshells... ." that's a good one there's another one I liked that you might want to check out too, "Overcoming Borderline Personality Disorder: A Family Guide for Healing and Change" by: Valerie Porr M. A. Getting a good understanding of what BPD is, is a great first step

Learning about BPD helped me to sort out what had always look like chaos into something I could understand, I began to see patterns in my SO's ex's behaviors.
You mentioned validation and that is an excellent skill to develop. You're right you want to validate her feelings not what she is doing. It's about validating the feeling behind her actions. Keep practicing for many of us this isn't a natural skill... .like anything else with practice it will become more natural.
Below are links to more information on Validation that you might find helpful... .
https://bpdfamily.com/content/communication-skills-dont-be-invalidatinghttps://bpdfamily.com/content/communication-skills-dont-be-invalidatinghttps://bpdfamily.com/content/communication-skills-dont-be-invalidatinghttps://bpdfamily.com/message_board/index.php?topic=210574.0I also want to point out the box to the right --> each item there is a link to more information so pick a topic that resonates and dive in.
Keep doing what you're doing... .support for yourself, educate yourself, and begin to practice new skills as you learn them. This is a process... .a journey... .and you are choosing to take action and work on your marriage this is a good thing

There is support, ideas, tools and hope here.
I know other members will be along to welcome you soon.
Take Care,
Panda39