It's natural for a hen to brood eggs this way, and to raise them on her own. She doesn't need food and water nearby. She should return home once a day to eat and drink, if her instincts are good. The exercise will be good for her. I wouldn't do a thing, since it's your neighbor's decision to leave her where she is, and it's his chicken. If she can't get to his food and water, I would put some out, but not hear her nest. I'll bet she is finding her own food and water source, even if she can't return home for this.
Happiness is when you can look at your chickens and smile....
Worry is interest paid on trouble before it comes due.
Flockwatching my little bunch of mutts, a favorite pastime.