>>110549863She's a government worker who lost her job. The movie takes place in the 80s, which was basically the end of the "if you work for the government, you're set for life" period within the US. She was bitter and broken down because despite sticking with her job, they still just ended up eliminating her position and her department anyways- not to mention, she's dealing with people like Arthur all day for jack-shit in terms of pay, but holding out because after a set period of time she would have gotten to retire.
Also, it's worth pointing out that mental health in general wasn't really taken seriously in the 80s. Today, if someone talked like Arthur to a psychiatrist- especially a government-mandated one- they'd be locked up in a heartbeat.