He then got upset saying that he asked a standard question that I should be able to answer.

She was quite upset on the suggestion that I will start charging late fee if she continues with this.

I am very upset with the management though.  

Understand there are limits though, because if you take too long or do shoddy work - who gets the upset tenant phone calls?

Now overall this would obviously mean I was charging less than current rental rates because even if I was at the current rate for my property, I would be giving them back 1/12th their rent per month at the end of the year, but if they stayed loyal and took care of my property and also with this gift every year would likely feel less upset over annual rent increases.Thoughts?

May not matter to you, or it may be very upsetting.  

If they're all on-time, paying tenants that have kept their units in good condition, there is no reason to upset any of them more than you have to.

Yet here you are asking if you can charge her rent and are upset with her for being abrupt. 

When I lay all this out for potential partners, they get all antsy and upset since they expect much more "profit" from their labours. 

Although in the landlord business of course your tenants are on a razor edge more than most home owners.. with lower rent areas of say 600 to 800 a month and 3X rent to qualify pretty tough to live on 1800 to 2400 a month for most folks and one little upset and boom