Unfortunately I have no advice, but just writing from my own experience. My mum (who's 81) was on a mental health ward before I even knew anything was wrong. Her sister rang me to tell me this. Even then I thought she was just 'in hospital'. My aunt had mentioned various times over the previous 12 months that I needed to get PoA, but everytime I spoke to my mum it was my aunt who was making a fuss over nothing. For obvious reasons I didn't press the case with my mum that she needed to hand control of her finances over to me. In my mum's case there was no drastic event, but her neighbours had become increasingly worried about her. It didn't help that she'd been put on a high dose of steriods for an unrelated condition and I, like her doctors, thought she was suffering from 'steroid psychosis' (which, in the majority of cases, goes away when the optimum dose is found for the individual).
I didn't know her neighbours, so I was only hearing about what the family knew. A couple of things happened (being found outside the chemist's in her nightie when it was night), and it was the neighbours who got in touch with social services. I wanted to take my mum to my home from the hospital, but when that was mentioned they sectioned her. She felt tricked because she'd been assured that she was there on a voluntary basis (which she was, initially).
I know I'm not offering anything that helps, but what I will say is it's only when it can't be avoided that those who are there to help someone's mental health take action, if they haven't asked for it themselves. Perhaps that's a good thing, as once you get into sectioning and care homes you're taking away someone's liberty to live their life as they want to. I'd say just carry on doing what you're doing. My mum would have perhaps been in a care home sooner if she hadn't had her neighbours noticing what was going on. It's not like she didn't have regular contact with family, but it's very difficult to chose this for your own parent, spouse, etc, and I imagine whenever possible you pretend it's just old age.