For people not regularly around cats, odor is bothersome and difficult to eliminate. 

I was shocked when my carpet cleaner showed me the urine and feces damage to the property (he used a special light) and also he said once he started in to clean that level of damage the odor from the animals’ excretions would be released and become obvious throughout the house.

If it's the kind of mess that creates an odor or can attract pests (mice, roaches, ants, raccoons, etc.), it may cause damage to the property (e.g. wet items left on a hardwood floor), or it's visible to the community, then I make them clean it up and pass an inspection or I terminate their lease.You're not being the "bad guy" Landlord.

I also recommend inspections every 3-4 months until you're certain it's not creating any odor problems.

Upon sale, she will repay in full the loan she used to acquire the property.Although she might technically be in breach, I see this as no-harm, no-foul. 

That room does have carpet and even heavy steam cleaning does not permanently remove the odor. 

Its hard to do, but he'll come out with something bumbling...might even be the truth]"Well, no harm no foul, buy me a case of {??}

If you anger the tenant, they could sabotage your efforts or claim foul like saying someone stole form them.- I spend time during lease signing explaining to tenants that I will show the property after they give notice.

There is a strong urine odor in a couple of the rooms and also in the back yard. 

Holidays, Covid and foul weather did not help.