Michelle is an estate agent. She hears from her friend Jonathan that Sarah wants to sell her house. Michelle promises that if she sells Sarah's house and receives her payment, she will pay Jonathan R2 000. She phones Sarah and speaks to her assistant Thabo. Thabo is an employee of Sarah's and manages all her properties. Michelle offers her services in selling the house at the best possible price. All she wants for her troubles is R20 000. Who in this specific example is the principal?