In The Miracle Worker, Annie saw that Helen's parents often caved into her demands.  Annie knew that this was keeping Helen from properly learning and from reaching her fullest potential.  She knew that she needed Helen to be dependent on her alone, away from her family.  She suggested to Helen's mother that the teacher would have to "live with her somewhere else."  This somewhere else was a cottage on the Keller property.  The "garden house" was the perfect place because it was small and isolated from the rest of the family.  

Annie wanted to establish standards, expectations, and boundaries for Helen.  Up until her arrival, Helen's family allowed her to do almost anything she wanted.  This made Helen demanding and selfish.  She also refused to do anything she did not want to do.  Living with Annie in the garden house, Helen finally learned that she could not always have her way.