*welcome8
I hope we can provide a great venue to help you with your voyage of discovery

Lots of info and advice to be found here.
To address your point first that your partner seems to be both on the money and yet missing the point at the same time.
Think of your partners mind as a huge library, but rather than all the work being stored in their complete volumes, her mind stores an enormous amount of snap shot photos and quotes, often with crystal clarity. The difference being they are not stored within the original volumes, but rather as a collection of like minded emotions.
Hence she can summon forth with convincing clarity all this "evidence" however it is out of context and massaged to validate her emotion of the moment. To others this "version" seems remarkably true and accurate as it does contain some insightful nuggets of truth. But in reality it is corrupted by the rearrangement, and enforced with a confident hard sell. This can even leave us feeling doubtful about our own recollections and view of reality.
Why can this disorder go undiagnosed for so long is a good question. It is a hidden disorder, it is very common, yet few people have even heard of it and in the majority of cases it's never diagnosed. As a result we have no idea how to deal with it as it is counter intuitive, everything we do seems to make it worse.
Luckily the information we have here is a balance of clinical studies and the collective empirical experience of thousands of members who have been through this.
Waverider