I was in this situation once. An elderly man on our street suddenly became more frail after a stroke. Daughter - only child - was making her way up the ranks of the army very successfully which meant she was away for long stretches of time. No one's fault. It was just the way it was.
It started off ok. But then we somehow became the default hub through which all messages and appts and schedules were filtered because we had the spare key and the cleaner and home help had to be let in, we started doing food shopping, taking stuff to the laundrette for service washes. We were the emergency contact when he fell a couple of times. Then we were visiting him in hospital. Then we found ourselves stocking his freezer, and making sure his home was comfortable to come back to.
It was fine at first. He was a nice gentleman who had brought us apples and runner beans from his garden. We in turn felt it was what being a good neighbour was about and we were lucky enough at that time to live on a street where people did look out for one another. But we started feeling uncomfortable. Partly because, in the absence of anyone else there, we had been forced to assume an intimacy with him that he didn't necessarily want and he was a proud man. So we were sensitive about that. And he obviously would have preferred his daughter there, rather than us.
The thing is with these sorts of situations is that, by definition, they don't improve, things gradually get worse. I felt sorry for the daughter because had she been a man, I felt everyone would have accepted her being away in the army and there wouldn't have been the same level of expectations on her. At the same time, it wasn't really my responsibility either, and DH and I were busy with our own work and dc.
Things came to a head one weekend when he ended up very briefly, post minor op, in intensive care and I rang up to find out how he was and the nurse in charge told me that my name was listed as "first contact" (even though his daughter was informed and knew all about the op) and as it turns out, she was overseas again, having left that morning. I ended up visiting him in hospital a couple of days later and taking him in the things he needed, for which he was grateful, but that evening I rang up her army base, sat there on the phone for 40 minutes being passed from pillar to post and eventually got through to her at her posting, and told her that this wasn't on and she couldn't rely on us for help any longer and she needed to sort something out. Only then did she take leave and come home and actually do something, which unfortunately or fortunately for him, whichever way you look at it, was that he moved in to a nursing home. Things would have been much better overall, especially for him, if she had taken responsibility sooner.
It's all very well people saying "you don't know what kind of relationship they had with their parent" but surely you as a neighbour don't have a relationship at all other than one of passing friendship, and in circumstances where an elderly person can't look after themselves any more - which will happen to many of us btw - someone has to look after them and see they are ok. OK as in having food, water, basic hygiene and necessary medical care, we are not talking about frivolities here, anything above the basics is a bonus frankly in these sad situations. I don't believe in passing these things off on to the state to sort out because invariably, from my direct observation, they don't tend to do it very well.