Can a non-owner lease and property manage?

[Jim Bentley]

I'm in Oklahoma.  My mother-in-law fully owns around 30 properties which I and my wife have been leasing and managing for a couple of years after my FIL's death.  I was recently told that the laws say that ONLY the owner of the property may lease and property manage.  If she want's anybody else to do that work, they have to have a realtor license.  My MIL is unable to do any of this because of health, and she doesn't want to pay a property management company.  

Is what I was told true?