mcdonnell’s family should file a civil suit against her.
I don't know if he has any surviving family, but even if so, they'd have zero chance of success. If the Federal Government couldn't bring the investigation to trial when they reopened the case in 2003, a civil suit would be doomed.
Then there's the issue of lawyers' fees -- if you read the kron4 series linked above, anyone bringing a civil suit would be facing an army of lawyers, as the federal prosecutor did, with all the time in the world to waste while jacking up fees for the plaintiff. Also consider that many of the WU and Black Panthers (the '71 murder was definitely a BP job, since the WU were too cowardly for direct gunplay) have since made it into respectable positions, even within the justice system itself, as per this description of one of those subpoenaed in 2003:
"He's an African American about 50 to 52 years of age, well respected in the community. [He] works in a government capacity -- in fact he's even worked at the Hall of Justice. He was referred to me by police officers who think of him in the very highest regard," says [lawyer] O'Sullivan.
Many of the Weathermen came from wealthy and powerful families, not least of which was Tom Ayers, father of Bill. It's been said that he was slated for a position in the Nixon administration, but Bill's antics ruined his chances. He was liberal Republican at best, and it's not inconceivable that he had a hand in his son and DIL walking away from their crimes, "guilty as sin, free as a bird."