She did a couple of individual sessions a few months ago when we tried to start some marriage therapy... As a matter of fact she told me the counselor even said specifically not to let anyone try to convince her that she has a personality disorder because she definitely didn't. This was after one meeting with her I believe.
So the information source was the patient, not the counselor? Since your spouse is an interested party (the patient) do you have enough trust that the counselor would concur? Or was this her version. After all, she agreed she has BPD but her counselor, the trained professional, says not?
Be aware that in the past - and probably still today - many professionals are wary of diagnosing patients with BPD since a common reaction is Denial and stopping sessions. Oh, she stopped after a couple sessions?
The one thing she focused on the most was that it isn't curable. So basically she seemed to come from the perspective that she has it and there is nothing to be done about it so I'm just gonna have to figure it out because I'm still in the wrong.
But meaningful therapy can improve perceptions and behaviors. It's all up to the patient.
One of the most respected authorities on BPD therapies such as Dialectical or Cognitive Behavioral Therapy (DBT or CBT) was Marsha M. Linehan who late in life revealed that earlier in her life she had BPD but through grit and determination she had managed to find ways to recover.
In past decades it was not uncommon for people with BPD (pwBPD) to be diagnosed with Bi-polar because it was billable to insurance and usually treated with drugs as a chemical imbalance. On the other hand, BPD was viewed as largely untreatable until
Marsha Linehan, herself having suffered with BPD, developed therapies such as Dialectical & Cognitive Behavioral Therapies (DBT and CBT). Alas, as you've already discovered, applying meaningful therapy in one's life is very hard for a pwBPD.
https://psychcentral.com/blog/marsha-linehan-what-is-dialectical-behavioral-therapy-dbt#1