Hi daveym10,
Welcome and hello

Last night sounds pretty scary for both of you. Amazing that she called the ambulance, and worrisome that she called the police. How were things when you returned home?
Not all BPD loved ones become violent, but it sounds like your fiancee may be prone to physical aggression. Has she done anything like that before? What events led to her diagnosis?
While you wait for her treatment to begin, there is a book that might help called High Conflict Couple by Alan Fruzetti that uses DBT techniques to de-escalate conflict.
Can you tell us more about what happened right before she grabbed you by the throat? Sometimes it's easier to work with an example and go from there, to point out some communication skills that could help in those moments.
Many of the skills are not intuitive and must be learned.
Glad you're ok, and things didn't get worse than they already were for you.
LnL