Yes, well, when one is deeply depressed for long periods of time it plays havoc with one's sense of reality. You ask yourself a lot of questions and they all seem to come up with a negative answer. It literally seems like every door is closed, and there's no way out. I've been there, and that's what it's like.
Not that there isn't an awareness that your own thinking is disturbed...there is such an awareness...but it just adds to the overall feelings of hopelessness and worthlessness that are pulling you down.
Depression is the most insidious and tenacious thing, because by its very nature it tends to keep adding more weight to the load, so to speak.
Some people break under that strain, while others just quietly retreat from life a little bit at a time.
This woman obviously broke. By all accounts, she was a very likeable and gifted person when she was in High school. The whole thing is just utterly sad.