Hi. Welcome to our family. I am so sorry for what brings you here.
You and your daughter have both been through such a lot. Suicide of a loved one is a terribly traumatic experience and I am sure it has taken a toll on both of you
BPD is a very serious mental illness that is not easy to understand. Personality disorders in general can be difficult to comprehend. It is usually obvious something is "off" but most people do not know what personality disorders are, how to spot them, or how to deal with them. Even therapists trained to deal with personality disorders such as BPD often see their own therapists because it is difficult to deal with these kinds of clients.
I know that you must feel a lot of guilt and ask questions like "what if...?" to yourself. Please know that you could not have inherently known what to do or that your wife would have taken her own life in such a way. It was her choice. Even if you had known about BPD it may not have changed the outcome.
I am glad your daughter is in treatment. With sincere effort and participation in therapy, BPD is a treatable disorder. That is encouraging.
Do you see a therapist yourself? It may be helpful for you to process your wife's passing and also to help support you in supporting your daughter.
How can we help you? We are here, and listening, and once again, welcome.