Gal bully my son

There is a gal bully my son at playground, she even calling him far boy making other also calling like that. Today she asked me to borrow her hand phone I said no to her because she is rude and never appologise to my son. Other than that she is total stranger she is not local and she been checking out other children house, one time she follow a gal back and says like to go in her house to use toilet. As we know we don't simply let stranger in the house, some more she's not local. She told me she wants to call her mom, well she can go home to call her. Instead she followed us lucky I stopped and she also stopped or else she would want to come in my house. She saw somebody she knows and run up to the person at playground. She has been playing with other kids in playground I don't see her going to their guidance to borrow hand phone. We will see what happen tomorrow.