In a former life I was responsible for creating a billing system for a municipal utility (customer service manager) and what you describe is somewhat common.As an investor, and separately a CRE professional, I've had to confront this issue.The cleanest way to handle this situation is to install a sub meter to measure specific usage e.g. the unit or the common areas.

She’s young and non-confrontational I don’t want her to be uneasy everyday about whose she’s living next door to because it escalated into this whole situation.

They left me in one piece and it was shortly thereafter, I ceased any such face-to-face confrontations and stopped letting my wife show the apartments.My phone interview includes enough information that I am able to do a courts check and check the local landlord assoc "don't rent to" list.

I used back ground checks (public offender sites) to find out about their past,  I did talk to them and confronted them about it, but I have made my decision.........  

Not only does it let me sleep well at night, but I wake up with enthusiasm, eager to confront the challenges that each day brings.

When confronted they said they were not paying so I evicted them.  

They can't simply brush you off when confronted with the evidence.

They may not know they are interested in a deal until they are confronted with it.

The conversation should not be confrontational at all.  

It can absolutely be for self-defense, but they are the great equalizer when it comes to confronting and neutralizing the threat.So I stand by my original statement