May be worth discussing the issue with a therapist yourself, one who is well-experienced with BPD.

I'm surprised there aren't better materials on how to move a BPD wife towards therapy. E.g. how long do you practice validation etc? What should her emotional state be? Etc... .
We all understand your desire to see your wife get treatment. It would be great if she does, and maybe she will. She's a psychologist, so she may be more (or maybe less) open to idea that therapy is a good thing for her. But for therapy to work, she has to accept that she has a problem and then commit to the treatment. Some people with BPD have this insight and follow through, others don't. Wether she gets treatment - and really commits to it - is up to her.
If this is a deal breaker, you can ask her to get help using DEARMAN. It's been done. Same with ultimatums. Sometimes it works and they get help because they know they need it. Sometimes (most times) they say no. Sometimes they go to therapy for a while because they feel forced into it but only go through the motions. You know your wife better than us, this isn't one size fits all stuff.
For your sake, I hope she gets treatment. I also hope that you don't put all your eggs in this basket. What's your next step if she says no? Just remember, there are ways forward even if she never gets treatment. Those are the ways we mostly focus on here.
Let us know what she says. I'm pulling for you!
Oh, and if you do ask her to get treatment, its best that you focus on the behaviors that are causing problems and not mention BPD.