Ah, by "reason", you meant the grandmother's reason!
Yeah, I don't think that's a good reason neither. Now, it not being a good reason is not a pass to act against her will either.
I think OP needs to convince her that it's a bad reason first.
> That's because 'I want to die' is a valid reason. Or at least it should be
That's a very reasonable reason not to want to take a pill, but that's not even necessarily the actual reason. Often the reason is completely unknown. Possibly the person refusing the pills doesn't really know why they are refusing it / doesn't even have good reasons. The actual reasons behind the refusal doesn't theoretically matter much in whether they should be forced to take the pills. They should only matter to convince them that they should take the pill for their own good. (the reality is probably more "dirty" than that though)
> simply acting against autonomy is itself bad within their framework, but this is inconsistent with society's behaviour at large.
Possibly, but, depending on what you mean:
* society at large acting against autonomy isn't necessarily a good thing / a good justification for doing it. Society at large needs a fix.
* fighting fire with fire is not necessarily the right approach