I agree with that statement 100%. But you must also consider the fact that people react to this information as possibly just another future excuse to help this parent skate out of the consequences of a guilty verdict. Which I tend to wonder myself when reading cases like this.
Yes, depression is sad, but some people are just getting sick of people claiming insanity, depression, or whatever after they commit such heinous crimes. I don't know about this case in particular, but I wonder with most of these kinds of cases, if it was so apparent, why didn't the criminal seek help before the crime was committed? Or better yet, why anyone that it was so obvious to (before the murder) like friends and family, 1/3 of the time never say anything until after said crime is committed?
If this mother did seek help and did not recieve it, or family or friends tried to alert proper agencies to a problem brewing, that is very sad, but still doesn't deflect the fact that she murdered her child. Even if she has depression, I have no sympathy for her unless it can be shown she was outright loony, which I doubt. But before this is over, I'm sure we'll all know.
If depression is a good enough excuse to murder someone, then I would suspect that at least 1/3 the population of the United States could be murdered tomorrow.