Has she demonstrated responsible behavior since?

There is plenty of room for unethical behavior within that realm.

To over-simplify, I think screening is a great way to understand (a) are you who you say you are (b) do you pay your bills and (c) is your behavior worthy of this expensive asset?  

Also, I would make sure to communicate a little via email or text, so you can have some physical evidence of his behavior.

For all we know he had multiple affairs and that led to his divorce, so he has reckless behaviors that led to his financial issues.

You need to re-establish with the tenants new rules of behavior.

I have been attending college for about four years; I obtained my Associate in Science, I conducted behavioral research as an intern for one year, I became Vice President of Leadership in Phi Theta Kappa local chapter, and I was active in school activities.

If not you will notice a shift in attitude.Instead we tie good tenant behavior to a discount in rent, movie tickets or something that says "we appreciate that you are a good tenant".

His longest running tenant was 25 years.I know investors that give away TV's for the same type of behavior.

All too often, new investors either overdevelop or spend their money too fast - both of these behaviors derail their plans and stops them woefully short.