Hi JillS, and
Parenting a child with any sort of mental illness, be it BPD or otherwise, can certainly be a struggle. Sometimes love isn't enough to help them through their difficulties... .but you are right, getting a proper diagnosis can be the first step towards help and healing, and it is good to hear your daughter is going through this process.
You are also right in that there are many folks on this site that can share a wealth of knowledge in regards to dealing with a loved one suffering from BPD--you've joined a community of caring individuals, and there is a lot of help to be found here.
Rapt Reader gave you a great resource to check out. There are plenty of senior members experienced in parenting a child with BPD, and they can offer plenty of advice and tools to help you better communicate with your daughter.
Please let us know if you need help finding anything on the site. Keep posting--we're glad you found us!