The baby is young enough that it is possible that the mom is still suffering from some sort of severe postpartum depression. If a doctor was trying to help her by trying different medications it could be a bad reaction to a new medication. Or, if she was on a medication that seems to be working but missed a dose or two or ran out of it that could have a very bad outcome as well. Even when a doctor decides that a certain anti-anxiety or depression medication needs to be stopped they wean a person off of it because stopping it suddenly can be disastrous.
That still wouldn't explain why the husband didn't have the decency to try to find her or report her missing, unless he did but police aren't telling the public. I can't imagine why they would keep the actions of a normal loving husband or any family member a secret. Of course one very common cause of severe depression in women is living with an emotionally indifferent or cruel man. My doctor, (a very well respected and experienced male doctor) told me that. MOO