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.