I’m sorry, but I have to disagree. Living with mental illness myself, as well as a neighbour with mental illness, I am tired of the attitude that people struggling with mental/emotional illness/injury are considered either “less than” (meeding to be treated as incompetent children) or damaged (unable to exert any control). Given, there are many illnesses that do affect a person’s behaviuor, and that needs to be considered. However, excusing a person simply because they bear a label of “mental illness” is not, in my opinion, helpful to them or appropriate in the larger context. We all have the right to be treated with respect and dignity, and refuse to accept behaviour from others that is not in line with this. There is nothing wrong with politely but firmly telling anyone, be it a child, employer, alcoholic/addict or someone with a “mental illness” that you will not accept being yelled at, sworn at, or verbally abused. Not doing so only tells the other person that you will accept the behaviour, and it will continue. It is not judgemental, it is insisting on being treated with respect. If a person is unable to interact with appropriate social skills, they will be isolated, and this does not help a person with “mental illness”, and permitting intrusive/aggressive behaviour/language leaves the door open to escalation. It is entirely possible to let a person know that you are willing to converse with them and/or help them and also make it clear that you will not tolerate rude/obnoxious/aggressive behaviour/language.

Surely the neighbor isn’t always nasty. Surely
someone looks in on her, helps care for her. Is
it that hard to talk to the person who looks in
on her, or to wait until she is calmer and talk to
her yourself? In my experience, the best thing
for lonely people (and she must be lonely) is for
someone to reach out. Ofcourse, if you feel frightened or think you would be putting yourself in danger, don’t do it. But the key to the problem might be simple courtesy and conversation.