@Bob Malecki  Please excuse me, I am coming into this conversation a bit late!

If they can't find a senior home by then, I would say they have no excuse. 

@Jim Adrian Please excuse my ignorance.. what items fall into "normal wear and tear" exactly? 

If she cooperates through all of this and the buyers do their final walk through and she is still there (I'm sure she will have a great heartbreaking excuse), you are now getting sued for breach of contract because you stated the place would be vacant.

If it's medical that's often excusable provided their current income (minus their payments on these collections) still make up your income:rent ratio.

Excuse my ignorance, but why would YOU be required to pay a monthly service fee to Sub Meter solutions (other than the fact that their deal requires it)?

For instance, think of a favorite coach you had or a teacher you loved, but you knew would say no to a silly request or excuse - so you just never went there.  

People always bring up possible retaliation but it is an excuse for not dealing with the issue personally. 

When they have the one late payment, with every repair, with every excuse, issue or bump in the road - you will be thinking - "I KNEW IT, I should have followed my gut."

I charge 10% on the balance after the grace period and never waive it because then they think they can get away with making excuses.