It appears the tenant has a disability and so the dog really is a service dog and not one of those comfort dogs. 

If only some tenants receive default letters, then you run the risk of some tenant claiming you treated them more harshly because of their race, familial status, disability, etc.Good luck! 

The violence and disability/language barrier has made this a more complex issue than I think I can figure out on my own.

A vacation or other short absence counts as time you lived at home (even if you rented out your home while you were gone).If you have a disability, and are physically or mentally unable to care for yourself, you only need to show that your home was your residence for at least 12 months out of the 5 years leading up to the date of sale.

To me, this admission may disable you from getting your deposit back because you are naming reasons for renegotiation outside of your contingencies.  

However the owner is a 70 year old disabled veteran.

These statutes don't include any periods where the owner was legally disabled."

However, I believe you are referring to what Illinois refers to as the Adult Guardianship program, where the county is actually administering the estate of a disabled or incompetent adult.  

Not elderly or disabled. 

Were you discharged with any disability?