HELP! Landlord in need of advice!

[Jive Turkey]

Hey BP community, I just wanted to start by saying I really enjoy what this site has to offer and that it has provided me with tons of educational reads and that there is always somethin' good every time I log in.

Okay, so I'm trying to help out my mom that has rented out her house for 2 years now. We hired a property manger to get us a tenant in 2015. Lease/contract was for 12 months, we let go of the property manager and has been a month-to-month basis after that since Oct. 2016.

I have been out of the loop until now. We wanted to lock the tenant in with another 12 months contract BUT!! Come to find out this guy has been shorting my mom $250 a month since Jan. of this year! it's now the 10th month and this has gone un-notice by my mom! How is this possible, mother?!? UGGHH! Apparently she has been paying for the mortgage and not looking at her deposit from her tenant.

What can we do about this? ..Is there anyway we can recuperate the loss? I know I need to confront him, I just don't know what level to approach him with. Should I,

A.) Be abrasive and stern with threats to evict? 

B.) Be polite and see if he'll sign a contract to extend with the loss added to his future contract? Maybe wave all late fees if he'll comply?

I feel horrible that I haven't kept a closer eye on this but LESSON LEARNED! 

Need to settle this ASAP. Looking for anyone that is willing to give a little insight on this situation..PLEASE! Thanks in advance!