As several people have experienced, it's hard to impossible to get help when the person in difficulty is screaming out for it. From what I can tell, Caroline wasn't really engaging despite having struggled for years. She'd told the police she had no history of mental health problems, was seeing someone for her 'issues with relationships', but not her general mental health and continued to drink and possibly take substances.
This is exactly what people mean when they say that (in most cases) nobody else is responsible when someone takes their own life. Depression/suicidal ideation is a horrible hole to climb out of and it's hard but ultimately, nobody but the person experiencing it can do it. All their family and friends can do is offer support, and no matter how hard they try, sometimes that's not enough.
By the way, believing that Caroline was guilty of domestic violence doesn't equate to not thinking her death was a tragedy, because it really was. I just think it's extremely unfair to blame her partner for calling the police - he did the right thing, and nobody regardless of gender should be encouraged to believe that they should hide abuse because doing otherwise might cause harm to the abuser. That's how people end up seriously hurt or dead.