The thing that struck me as most odd, was when she would try to write a formal letter... .
WOW. What a revelation to me!

You see, when I met my ex, I had just moved to her country and didn't speak her language. She always helped my write formal letters. She would struggle for hours writing something like a simple e-mail to my landlord, that something in my apartment was broken. Something I would have jotted in 5 min in English or my native language. At the time I thought "gosh, this is really a complicated language!".
Just now, I found two letters she wrote on my computer years ago! One after her apartment was destroyed, due to a fault in a chimney, leaving the entire apartment and all her things cover in soot deposit (that was by the way what made us move together). The other is a complain about her mobile phone being disconnect because she didn't pay the bill. Yes, you read it right - SHE complained and faulted them for HER not paying her bill!

Now I speak the language quite well, and I am perfectly capable of writing an imperfect formal letter. And the wording that she uses is outright strange. Also, the tone is bizarre, considering in both cases she want to achieve something, yet the tone is hostile and aggressive.
Thank you for this insight! I think that moved me from 90% certainty that she is indeed uBPD to 99%.