I have a daughter with BPD, too. She first showed symptoms at about 22 years of age. She is now 40.
My wife and I have struggled for 18 years. We have had very many crises and ups and downs in that time.
We found it hard to get effective professional support. Many psychiatrists have been consulted over the years. Our daughter was often resistant to professional advice.
Fortunately, our daughter now has an excellent psychologist with whom she has made great progress using dialectical behavioral therapy (DBT). Importantly, she also has an excellent GP who liaises effectively with the psychologist.
Nevertheless, crises continue to occur. Police were involved following two recent incidents. A court case is pending.
My wife and I still struggle. We are still unsure how much support to provide and how best to protect ourselves.
We have two other adult children, one of whom has fled interstate to escape the situation. She tells us she will not be returning. This saddens us greatly.
In our society, mental illness is shameful. For that reason, carers are tempted to keep news of the illness to themselves. We ourselves did that, and it was a big mistake.
My best tip is to let in the light, and to do so early. Get as much external help as you can as soon as you can. Join groups like this one. Tell everyone. Shout it from the rooftops.
The needs of people with BPD must be acknowledged by the wider community. Families should not be expected to take on the crushing load that BPD imposes. Families who do take on that load enable the wider community to evade its responsibility. No family can cope alone with BPD.