Yeah. Towards the end there, I did too. The family never was that forthcoming with info and even admitted to wanting to keep some info from the children after she was found. I kind of wonder if AA didn't actually talk to her mom or someone and mention that she was afraid she was going to harm herself - and possibly even ask Mom or another family member to take care of her kids, but the family never wanted to let that piece of information be shared. (All supposition on my part & MOO.)
Regardless of her most recent relationship with the father of the two youngest, if it was reasonably predicted that he'd be getting sentenced to jail for some time the next day, she could have easily looked at that as, 1) anxiety/stress if it would mean loss of child support, & 2) a sort of freedom from worry that her kids would end up with him if she were no longer "in the picture". So feeling like he was going to prison for quite a while (assuming that she "knew") might have been the last straw that finally brought her to take that action.
Again, MOO.