I think this is a classic question in a specific context: the question of medical authority and treatment. If someone is infected with a disease you don't know how to treat and they are unwilling to be treated for it by someone that does know how, that is their choice and I think that from an anarchist perspective it ought to be honored. But, the question is complicated by the nature of psychological 'issues' and it's very difficult to provide a general answer. But let's get real about this... the history of how human beings have understood and responded to what we really do know now to be biologically reinforced psychological problems is shitty - really shitty.
So what complicates the question? The fact that someone's "choice" may not really be authentic. Ok, that sounds fucking elitist but let me clarify with an example: if I wanted to kill myself tonight and you knew that it was likely I wouldn't want to tomorrow and for a long time afterwards, I think intervention in my episode would be appropriate. What is important to emphasize is the recognition of how flippant my desire seems. There's a possibility that I finally worked up the courage to do it after a long period of contemplation; but, in that scenario I would think there really wouldn't be anything someone could do to prevent me from killing myself and the intervention would just be a delay - not that big of a deal. So while in that moment I may authentically want to kill myself, in general that is not really what I want to do and I may even be covering up a desire to be more lively, more in control of my life, etc. more than I really want my life to end. So, the value of individual agency is complicated by the fact that we don't always really act on our most general desires... or even our real interests.
So to get back to "getting real" what are the probable choices? Letting someone you care about or your community suffer, intervening into someone's relationship with themselves, killing them (maybe they're possessed by demons!), trying to personally delve into their world without the psychological tools that have developed over the past couple centuries, or trying to convince them that someone with those tools who may or may not be fulfilling the role of enforcing conformity with consensus reality can help them better. When you look at these choices (and sure, I may be missing a few), it seems clear to me that an anarchist ethic would be to do the best one can to take someone like ingrates advice... or because we don't have a solid mutual aid way of really helping people with severe psychological issues (let's face it, Soma Therapy and the Icarus Project only address some shit) to do what we have to do in this world: be fair with them in addressing your concerns and if depending on what you're dealing with, find someone who really knows how to help.
The problem really isn't that anarchist concepts of authority and consent create an ethical conundrum. The problem is that there isn't a mutual aid network for many issues. There are plenty of meet-up groups for a variety of people who are able to get out and socialize... though there's problems in that area because it's likely that the norm will be something like a bunch of people who are under psychiatric care and that may have the consequence of someone becoming convinced that not only do share the same issues, but they ought to share the same solutions. Regardless, who the fuck is to say that anarchists wouldn't be acting in an authoritarian manner via negligence due to ideological purity or some half-backed theory of human psychology? Aren't you already putting yourself into a position of authority by even taking up the question of someone else's problems? Is it a legitimate position to be in? It seems to be when someone is knocked out because of a tear gas canister to the head, when someone is getting beat up by neo-Nazi's, etc.
This is one of the things I really respect about Chomsky... his concept that the burden of proof is on the authority to convince someone of their legitimacy. That authority ought to always be challenged but in some cases it does seem appropriate. If it isn't, well then hopefully the authority will be critiqued and that critique will turn into a solution that doesn't require an authority. Anyway, that's my two cents. I personally have rushed a friend to a hospital when they attempted suicide and confessed later that they were having second thoughts. I didn't know how to get the pills out of his system. So whatever - I'd rather be a "bad anarchist" than know there may be help for a comrade and out of some abstract ethics, not attempt to find them help.