Stupidity: Ashley Judd finally tracks her husband down and what does she do? She doesn't try to capture him to prove her innocence, she doesn't notify the police, she doesn't take his picture and send it to every police dept in the US, she doesn't even follow him to find out where her son is. Instead all she does is ask for her kid back. What was she going to do even if she got him back? She is still on the run from the law, with little money and resources and she doesn't even know if her kid even remembers her.
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: As you said, she's on the run from the law. Why would she call the cops and risk going back to prison and losing her son again? Even if her husband was alive, she has no way of knowing what will happen to her. This was her best shot (especially in her mind) to getting her son back, thinking her husband would rather give up the boy's location rather than die; whereas height keep the boy's location a secret if all he was facing was possible jail time, if that.