Who is Isabelle Barney from 'I' Is for Innocent and what is their importance?

Isabelle Barney's is the murder victim in the case Kinsey is investigating. She was separated from her third husband and suffering from anxiety due to his harassment of her. Isabelle planned to go out of town the night after Christmas when her doorbell rang. Expecting her friends, Isabelle looked out the peephole only to be shot by someone on the other side. David Barney was charged and tried for the murder but was acquitted.