Hi Spacechase!
Welcome to the family
and congratulations on your upcoming wedding!
A bride-to-be! Enjoy the perks.
As a step-parent of a daughter who lost her mother at age 13 after a 4-year battle with cancer (and her brother who is 2 years older) I respect the way you are trying your best to be understanding and supportive and to educate yourself.
You asked for additional resources, and I just want to say that I am so happy that you found us and hope that you will stick around as you try to work this out for the sake of your upcoming marriage and new family. I strongly recommend and support the idea of educating ourselves, reading the right books and participating in webinars. Having said that, even if you go so far as to become a therapist yourself there is no magic cure. You likely already know that you are not going to "fix" her, you can only adjust your reaction to her difficulties. Do you think that you can have the strong mind of being able to not take anything personally? Do you think that you can live with her hostility without becoming angry yourself? Be happy when she is happy, without riding her rollercoaster and being upset when she is upset? These things will be vital to your marriage as you will have to support her father as he tries to do the same. There is a book called "The Four Agreements". It's an awesome book, not necessarily about BPD but it does teach about not taking anything personally.
One of the professional authors of the recommended books (I can't remember which one) suggested that we do not "fragilize" our BPD loved one. Your future step-daugher sure does seem fragile, does she not? Do you think that her fragility has given her some power in this family until now? Wouldn't it be great if she could be empowered by something else? Easily said, I know. It will be hard for her to let go of this power unless she has a distraction which may or may not happen once she starts school.
Her dad can certainly look to the heavens and tell her mother that he did his best, gave her everything he could until adulthood. He certainly made sacrifices. Going forward, it is his turn and his time to "live" again. There are three lives at stake here and as Swimmy often says "everyone in the family is equally valuable". Or something like that, sorry if I misquoted you Swimmy!
If you think about F.O.G. (fear, obligation and guilt), think about how you might define your FOG. How might your fiance describe his FOG? Don't feel pressured to answer that here, although it could be a great discussion.
I wish you all the best, and I hope you can stick around! There is so much more to share with you, so much more than we can write in one post.
Cheers,
R