If your mother is looking to be a renter, she can find any agent with whom she is comfortable. An agent's commission would be paid by the owner/landlord, so in essence and agent's services would be free for the potential renter. The agent she chooses should have access to all the MLS listings, which would provide her the greatest number of potential places in which to rent.
Hope this helps, and good luck!
Alan Kurpiewski, REALTOR
CA BRE Lic. 01912043