Stupidity: When Libby finds out her husband is alive in San Francisco, she calls the insurance company to tell them. Why didn't she call her lawyer who could have looked into this and actually done something about it?
Stupidity: Nick tries to get rid of Libby once and for all by sealing her in a coffin, but he never even bothers to properly check her for anything that she could use to possibly escape, which she ends up doing with a gun.
Suggested correction: It's never stated that she was charged with 1st degree murder, nor that she killed her husband for the insurance money. It was only brought up in trial as motive. Nick's accident was ruled "wrongful death" and the fact she did get paroled further show she was never convicted of 1st degree murder.
And what about the phone call from prison the Libby makes to Angie, and Angie says she "was just about to call her" or she tried calling her like how the heck can you call someone in prison!?