I am not excusing her. Yet the dynamics of an abusive environment can lead people into inexcusable behavior that they would otherwise not take part in.
Bear in mind the framing of your question carries much judgment within it: asking if she “just” messed up, The attorney did not say she “just” messed up, that would be minimizing her acceptance of responsibility.
And saying she “allowed” her children to be abused implies full ability for her to exercise discretion, yet does not describe what dynamic was going on in the house. She is accepting responsibility for her part in it, and going to jail. She is not getting away with it.