In act V, Eliza acknwledges that she can never return to her former life "back to the gutter." Why does she feel this way?
Eliza has been exposed to an entirely diffrent lifestyle through the efforts of Henry Higgins and Colonel Pickering. Her changes in appearance and language have made it possible for her to interact with such people as the Eynesford-Hills. But more than that, she has changed on the inside as well. As she tells Higgins and Pickering, "I was brought up to be just like him [Higgins], unable to control myself, and using bad language on the slightest provocation. And I should never have known that ladies and gentlemen didnt behave like that if you [Pickering] hadnt been there."
Now she has developed self-respect and a taste of what a gentlewoman's life could be like. She later compares herself to a child who is brought to a foreign country and in picking up a new language, forgets her own. She has adopted the language, the manners, the dress, but most importantly the self-respect that will not allow her to resume her life in the gutter. She knows she is capable of much more, a much better life that being a flower girl. She now has options that she never had before. She can work in a flower shop, she can teach others how to speak properly, she can marry Freddy. With the education that she has received from Higgins and Pickering, she can improve her lifestyle, and she fully intends to do just that.