Well, obviously, I could be wrong about the whole thing, yet my impression of the day was what I said. I wasn't trying to blame the brother, I am not about blame. I think that Diane had BPD (or something very similar) because she was abandoned by her mother at 9 and grew up in a family that was all men. She was forced to be the caretaker of her brothers and probably her father too. She built a life (based on the documentary) in which she had to be the perfect mother and, essentially, the mother of her own husband. She also built a career in which she was in control. My feeling is that if she did have BPD or emotional regulation issues, the behavior (the drinking) and its effects made it more difficult for her to control her impulsiveness. The NY mag article cites 2 incidences in which she was extremely impulsive. It says:
"Though Diane could be impulsive, Danny never doubted her judgment. One time, Diane ran out for milk and returned with a flat-screen TV. Another time, she went out for groceries and returned with a Jeep Cherokee. “She deserved it,” Danny tells me."
http://nymag.com/nymag/features/62043/index1.html
I get the feeling that, based on her history, she was living in what mentalization therapy called "pretend mode". She was faking her way through life, building the image of being in control, the perfect mother and employee. The friends in the documentary say time and time again how she exhibited black and white thinking, burning bridges with friends and family, and how she either liked you or expressed her dislike in a dramatic fashion. This behavior is a hallmark of BPD.
People with BPD can get triggered into extreme behavior based on their dysregulated emotions. There's a lot of shame associated with BPD. When that shame is "touched" by friends or family, the person can make wildly dangerous and irrational decisions, behaving in ways that others can't understand. I think it's possible that her shame was triggered in the phone call, which, from the brother's perspective was a completely natural reaction - I mean, what if your sister was drunk and had your 3 daughters in the car?! It's only natural to go ballistic on her. I know I would - out of worry and concern for my three daughter (which, BTW, I have 3 daughters). When her world came crashing down around her because of her behavior, my theory is that she said "f*ck it, I'm better off dead" and, in that state of drunkenness, made the decision to kill herself and the kids. I know it seems completely irrational and almost evil, yet when someone is emotionally dysregulated like she probably was, the irrational rules the day.
Of course, like you all said, we will never know for sure. My point in posting all of that was that the other potential Diane Schulers out there need to be offered compassion and, hopefully, treatment before they get to that mental state. Unfortunately, there are probably quite a few considering a NIAAA study showed that 5.9% of 39,000 interviewees exhibited signs of BPD.