Welcome, we are glad to hear from you. Is your daughter in treatment/ therapy ? Please peruse through this website . I would say also start with this link
https://bpdfamily.com/message_board/index.php?topic=114267.0I too, have a father with BPD traits undiagnosed and have a son 26 with BPD . I think the best thing you can do starting out is learning all you can about BPD. The library here has book recommendations on the subject, and a popular choice is " Stop Walking on Eggshells".
2 things to remember, it is a marathon, not a sprint. Unfortunately there is no "one thing" that will save the BPD child from the BPD. The second thing to remember is as human parents we have all made mistakes.
Please write back as you are able.