One key principle in this monologue is the powerlessness the narrator feels over daughter. There is a pervasive feeling of disappointment in this relationship despite the narrator's best efforts otherwise.
The iron of course is the most prominent symbol in the story, and it can be interpreted in a couple different ways. First, the iron represents the role of women and particularly, mothers. In this story, it also represents the chores that kept the narrator from interacting with her daughter Emily on a more regular basis. The repetitive back and forth motion of ironing represents the monotony of the narrator's emotions, desires and dreams which will never come to pass no matter how much work she puts into them, and the endless cycle of helplessness she feels.
Later in the story, the convalescent home in which Emily recovers from tuberculosis comes to have symbolic meaning as well. It represents the care the narrator could not provide for her daughter. Emily's balcony at this home represents both the physical and emotional distance between mother and daughter.