From what I've read about Broderick, she took a page from Jean Harris's book: His abuse made me suicidal, but somehow Dan & Linda got shot instead. Go figure!
Accounts of their separation & divorce seem to who Dan doing the right thing, using the law to deal with Betty's tirades & verbal abuse. One of the most damning articles about her appeared on a pro-Betty site. Even her advocates couldn't make her actions seem justified.
Jean Harris, incidentally, might have gotten her defense from Alice de Janze who in 1927 shot her lover, Raymond de Trafford & then herself in a Parisien cab after he tried to leave her. Both survived. The French public & court were so taken with her story, she was hors d'amour, said the court, & she was let off with a fine (it didn't hurt that de Trafford, after he recovered, gallently claimed the shooting was an accident as he tried to stop her from shooting herself).
The trope of the woman wronged, turning all blame on herself before accidentally shooting her erstwhile lover isn't new. And I honestly don't know if Harris was aware of de Janze or considered that story in her defense. But it seems possible. And even more likely Broderick was inspired by Harris when claiming she had gone to her ex-husband's house only to kill herself.