I haven't voted at the time of writing this but my view is:
it is perfectly reasonable for anyone to spend and distribute their own money as they wish. so on that principle I should vote Yanbu.
however (a) it is unreasonable to try to control the major life decisions of adult children by any means, including financial pressures and (b) you cannot buy love. if her adult children find that they don't want to see that much of their old mum then she has made her own bed.
if ones child grows up and then pursues a career that takes them to the other side of the world that is certainly distressing but our job as parents is to first give them roots to nurture them and next give them wings so they can fly. chaining them to the nest isn't good parenting.
and however much the adult children in question may love and want to see their mum, they will have other things to balance- their own career, the family and career of their life partner, and the education of their children. these priorities may make a different place to settle a more sensible decision.
given the scale of the resources that your acquaintance appears to have, a better plan would be to give each child a fixed sum equal to c. 10% of the cost of a family home in their vicinity, with no strings attached, and reserve the rest of their funds towards buying additional properties (maybe just small one bedroom flats) in the vicinity of the homes of any of their children who choose to live too far from her main home to visit regularly. she can then divide her time between these properties spending plenty of time and effort seeing her extended family wherever it makes most sense for them to live, for as long as her health allows.
she could sign up each property to an airbnb agency which will tidy, clean and arrange the letting-out of each property when she isn't using it, if she would like an additional income stream.