Anti-depressants are not happy pills. This is not the sort of thing I normally go about correcting, but it seems relevant here. Anti-depressants do not make you happy; they do not get you high; they will not give you an edge studying like some of the ADHD drugs that people abuse now. Anti-depressants take the edge off of depression. And if you've never been really and truly depressed before, a serious depression is far out of the range of normal human experience.
Second, stress and mental illness are intimately connected. Stress can exacerbate an already existing mental illness, or can cause the first breakout episode of a mental illness. Habits that form during a time of great stress - habits of depressed thinking and depressed acting - may persist long after the particular stressors have faded away.
The movie depicts a woman who is no longer able to be outwardly normal. I have certainly experienced the sort of depression where outwardly you can put on a brave face but inwardly you are being eaten alive; but I have also passed from that into a more profound depression where the ability to function evaporates. I'm not going to fault a movie for depicting someone who is nonfunctionally mentally ill, though I do think it's a pity that there aren't more portrayals in film and literature of the functionally mentally ill. It would be nice, just for me, to get to see more!