It is a way to keep people in their homes after they have retired instead of the elderly being priced out of their own homes. 

One very nice elderly lady stayed at the property for many years.

Example would be elderly parents moving in below kids, brother/sister in law with kids moving into unit next door with family with kids of roughly the same age, etc.

Does your tenant know that this is going on as she is elderly and ay not be aware of what going on outside.

The first group are usually elderly and need the subsidy to afford rent on their fixed incomes.  

Some protect the elderly by not reassessing until property is sold, others reassess every few years.

We have "elderly" SFH (most close to a decade old) and put in high efficiency (1.1 -1.2 gpf) toilets from Lowes/Home depot that only run about $100 each. 

The owner is an elderly widow who is refusing to accept any offer for her house because her deceased husband advised her: "if something happens to me, don't get involved with the rental properties." 

The current owner is an elderly woman that no longer wants to maintain the property after her husband passed away 3 years ago.  

My elderly aunt wanted to give her the opportunity to sell her land.