Miss Dulcie treated Annie John with criticism and detest. Annei says that she was treated like a servant who was made to sweep the floor instead of sewing. She also says that Miss Dulcie would always criticize her even though she did exactly what she wanted her to do.
By “the dustheap of my life", the narrator means that she is putting all her anguish over Miss Dulcie behind the past and moving forward in life. "Dustheap of life" is being referred to as bad things that happens in our life which we need to let go.
