My 18 year old daughter is in a psych ward after cutting (again), and called me tonight to say the psychiatrist definitively thinks she has BPD, which seemed accurate to me after reading about it, except for the part about having trauma in her history. 

I believe she was raised in a normal if not nurtured way. She believes she was traumatized by emotional and physical abuse (spanking), and that her 2 siblings ganged up on her, and as parents we let them. I have always thought my kid were well loved and yes we spanked them, but rarely. I can remember 3 maybe 4 spankings with a thin wooden kitchen spoon, on all my 3 kids, during their childhood, and not just her -- and it was because they were all 3 in trouble, and all 3 got spanked. She was absolutely never singled out. 

I read up on spanking tonight, and was shocked to find dozens of articles saying this is indeed severe abuse and can cause mental illness. I need to understand this. The more I read the sicker I got. I feel like a monster. And I also don't understand why I never second guessed it. In hindsight, I am not the kind of person to hurt another so I can't fathom why it seemed normal to spank my kids. I know for a fact they were never injured from these spankings, but now my daughter is saying 10-12 years later that this was both physically and emotionally traumatic, and caused her mental illness. 

Can someone tell me if spanking a kid 3-4 times with a spoon over their lifetime can cause them to develop BPD? 

She also said she was invalidated by us frequently telling her to stop crying as a child. She cried all the time for what seemed like very inconsequential things at the time. She was always finding a way to get hurt and then she would sob inconsolably. I remember reading book after book about the highly sensitive child, trying to find out how to stop her frequent crying, which was something she did from early days. Since she had a twin, it was even more pronounced because one was happy and well adjusted and friendly to all, and the other was fussy, and tearful and always finding something to cry about. It was stressful. 

How can I unpack this to understand it better? Also, I'm hurt and mad and confused by her accusations but trying to stay focused on how I can best help her right now. After all I heard tonight, I feel like I ruined my child and I want to tell her I'm sorry, but I also don't think I did anything so horrific as a parent that would cause this. But yet clearly I did. Can someone break it down for me?

I have spent the last 8+ weeks almost every waking hour running to and from hospital after hospital as she checked in and out of 4 emergency rooms, 3 PHPs, and residential. Every day, 7 days a week I have gone to be with her to help her. And tonight she laid this down hard on me. Right now I feel like everything in my life has crumbled. Do I keep trying to be with her and help her through this; or if I did this to her should I leave her alone to heal away from her family. I'm so confused and terrified right now. Would welcome any experienced insight. 