Convict or not to convict

There's a story of Clara Harris who killed her cheating husband by running him over several times in a hotel parking lot. There are campaigns trying to get her released, saying she was justified in what she did. I don't condone adultery, and I can sympathize with the wife and children on the break up of their family, but is it right to free a woman after murdering her husband? Is it ok for people to take the law into their own hands? Did David Harris get what he truly deserved? Should the state get involved in marital affairs? Seems like a no win situation in this case for the Harris family.