How we cite our quotes:
Eliza enters, sunny, self-possessed, and giving a staggeringly convincing exhibition of ease of manner. She carries a little work-basket, and is very much at home. Pickering is too much taken aback to rise.
LIZA. How do you do, Professor Higgins? Are you quite well?
HIGGINS [choking] Am I— [He can say no more]. (5.115-117)
Here, once again, Higgins is stunned to find that his "creation" is now able to control and change her manner with ease. That said, Shaw's use of the word "exhibition" casts the truth of that change in doubt.
Eliza. You see, really and truly, apart from the things anyone can pick up (the dressing and the proper way of speaking, and so on), the difference between a lady and a flower girl is not how she behaves, but how she's treated. I shall always be a flower girl to Professor Higgins, because he always treats me as a flower girl, and always will; but I know I can be a lady to you, because you always treat me as a lady, and always will. (5.143)
Ironically, Eliza argues that the man who taught her to be a lady will never see her or treat her as one. She also suggests that transformation is subjective, that not all people will acknowledge all changes.
HIGGINS. If you come back I shall treat you just as I have always treated you. I can't change my nature; and I don't intend to change my manners. My manners are exactly the same as Colonel Pickering's. (5.191)
In claiming that he can't change his own nature, Higgins complicates his own claims about change and transformation; if he can't change his nature, we have to wonder, how can he really understand how to change someone else's?