This is truly tragic. However, if she didn't present with suicidal ideation to her psychiatrist there is not much he could have done. It doesn't say the doctor's side. He probably did ask if she had a plan, ideation, means, etc. The meds she was on might not have been helping as much as her previous meds but she might not have been able to take them b/c of the risk to the babies. Often times people that have made up their mind to take their life often present quite the opposite. They seem as if they are at peace with their decision.
I'm really not trying to be too devil's advocate or stir the pot but I'm in the mental health field and work with high risk patients. Unfortunately sometimes suicidal patient's just don't report the severity of their symptoms and if they decide to truly end their life they find a way. My heart goes out to the family, friends, and the mental health professionals working with her. I wish they did see how severe it was.