My point appears to be going completely over your head. Caring for 4 small children, alone during the day plus working part time at night (even if its only 12-15 hours a week) is exhausting. Add the fact that she doesn't drive and therefore has to walk to either the school or the bus stop with the other three in tow, plus the fact that she suffers from depression, and its a serious issue.
Then, you rant and rave at her (and you admitted that you did) because the children accidentally knocked over a TV (and how did the children do that if it was properly secured?) and I can see how that might have been the straw that broke the camel's back for her.
My grandson accidentally knocked over and destroyed a 48 inch flat screen TV and while both parents were upset, neither blamed the other. They knew it was their own darned fault for not properly securing the TV.