I don't think she would have thought she could "thread the needle". Too many cars bumper-to-bumper in that intersection. As sad as it is, it appears that she may have done this on purpose, but her plans to kill herself were thwarted by the amazing safety systems and design of the Mercedes.
Having said that, I cannot judge her regardless of what we find out. To judge someone, you must be able to put yourself in their place and then say that you would have done things differently. And that's absurd because nobody can ever put themselves in someone else's place. If you could successfully put yourself into someone else's place, then you would, by definition, do everything exactly as they did.
This is what is usually referred to as a "tragedy". If it turns out that she did do this on purpose, and was capable of realizing that she would kill and injure others, then it's a lot like any other mass murder incident. Almost always, it turns out that mental illness was the root cause. I can't offer any sage advice about how to positively prevent these things, but better discernment of and treatment for mental illness seems like at least part of the answer.
As in most cases, even now I have too little information.