Need a thesis extension due to mental illness, but supervisor seems unwilling. How to proceed? &quot;Prependum&quot; clarification:
Strictly speaking, the supervisor has no actual authority in this decision (I think)-- it is between myself and the course convenor. However, I feel that `overruling' my supervisor by appealing to the convenor is unprofessional, and would inevitably affect the working relationship. This could be very counterproductive, and make an extension somehow pointless without the willing agreement of my supervisor. More importantly, they are the only potential academic referee (who knows me well) for use in a PhD application.

I know there is a similar question here, but I am looking for advice in my particular hairy circumstance.

The Issue
I am currently writing an Honours Thesis in an Australian university due in less than a month. Since the end of last year, I have suffered from severe depression (been to hospital; self-harm; seeing a psychiatrist; etc) and have made this known to the Honours convenor who has pre-approved any reasonable extension I might ask for.
The problem is with my thesis supervisor. They are highly averse to extending the project, as they are a very busy person. I understand this; it is not their responsibility. However, they also believe that obtaining an extension would be inequitable for other Honours students. I have made them fully aware of my condition, and stressed to them the magnitude of the impact it has on my studies. For instance, I (conservatively) estimated that I work less than half of the amount of time I would be able to if not afflicted. I also have had a meeting with them with several visible cuts on my arm.
Their response to my concerns is that regardless of my condition, I have made significant progress. They believe I am capable of obtaining a High Distinction with my current progress. It is apparent from their other comments that they do not understand what depression truly is (i.e. &quot;everyone gets nervous at the end of an Honours thesis&quot;).
At this point, I feel very pressured by my supervisor into submitting my thesis on time, but I do not think this is fair. I think that regardless of their perception of my academic performance, I have had dramatically less opportunity than other students due to my severe condition. However, it seems that mental illness is so poorly understood in this situation that what I think is a reasonable and fair extension (i.e. 6 months onto a 6 month thesis) is probably never going to happen in my institution, despite my gathering of evidence over the last six months in the form of letters from a psychologist.
On one hand, I recognize that it's not fair to ask my supervisor to continue supervising for the duration of an extension (and neither do I think they will willingly). On the other hand, I have been open and clear about the possibility of this happening from the very beginning of my project, and I believe they are seriously wrong about what they deem equitable. Their claim that an extension would be inequitable makes it clear to me that they are judging my condition based on my academic performance rather than on the actual opportunity I have had.

The Question
I'm really unsure what to do in this situation and would appreciate advice. Here are options I've considered:

With the aid of my psychologist, push for a significant extension that I believe to be equitable. This is problematic, as it is difficult even for me to judge how long that should be. Furthermore, my supervisor probably won't be available. If they are, they will be so reluctantly and perhaps begrudgingly.

Concede to my supervisor's wish for me to finish on time, and possibly end up with ~HD anyway.

Obtain a short extension (~1-2 months) and spend that time refining my thesis without the aid of my supervisor.
As you say, it sounds like your supervisor does not understand depression at all. Or at the very least, he or she doesn't realise that what you're experiencing is depression and not just typical thesis stress. That's very unfortunate, but all too common (in the general population, not just supervisors). You have every right to an extension.

However, given that you are depressed, you may not be the best judge of your own progress right now. Even students who aren't depressed have difficulty accurately assessing the progress of their research and thesis. Your supervisor has a lot of confidence in you, and seems to think you're "almost done". I'm reading between the lines a bit, but it sounds like your supervisor is a good supervisor apart from being clueless about mental health.

I think it might be worthwhile to have a meeting with your supervisor, and with someone who will be in your corner on the mental health issue (the Honours convenor, perhaps?). The three of you can then put together a plan to finish your thesis. Try to keep an open mind. I don't mean that you should let yourself be pressured into taking on more than you can handle right now. I just mean that there may not be as much work remaining as you thought.