IIRC, she didn't commit suicide, her death was accidental, and it was tied up with the story of the brother of character Ellen Burstyn played. It was an outstanding movie!
It was an outstanding movie, but I got the impression her death was suicide. She walked, or fell, into the river and drowned after months of agonizing over her crime (murder). And it was Burstyn’s estranged son she’d been helping. (Estranged because he was suffering from PTSD after service in VN.)
Anyway I remember going home crying over the ending because I thought it was so unfair.
But, I saw it a long time ago, and I could very easily have gotten details mixed up. It was a little fuzzy in the story in the first place, as I remember.