Act IV takes place later in the night of the ambassador's party, when Higgins, Pickering, and Eliza return to Higgins' home. All of them are exhausted and most of all Eliza, somehow she is the one who keeps silent and her expression is almost tragic. In the first section of act IV, there was only the two gentlemen's dialogue on how they feel about the whole thing and how happy they are that it's over. The two gentlemen totally ignore Eliza and do not try a bit to conceal their feelings before Eliza who is at the same time, actually taking down every word they say and at the edge of break out into fury.
Treating Eliza as nonexistent, Higgins has no feeling for her and that is when Eliza finally bursts into tears and throws the slipper at him, he still has no idea why. Eliza is so terrified about what's to become of her and can't hardly bear that Higgins only cares about his slippers. Most irritating of all is that Higgins is so indulging in his triumphant and did not aware that it's Eliza who gets him the slipper just like his unappreciative of Eliza's efforts in completing the work.
Eliza is so confused at her future. Even though now that she speaks like a lady, dressing like a lady and even behaving/acting like a lady, but there in real life are no realistic and financial support for her to keep the status. Though later when Higgins finally understands why Eliza is worry about and tries to comfort her, he, condescendingly but not heartily, is not really considering the whole situation in Eliza's position. Eliza being a independent woman does not want to live on a man, she wants to earn her own life just like she used to sell flower. For her, marrying a man a live on him is selling herself.
I'd like to give Eliza a praise that she decided to leave Higgins and did not stay to let Higgins support her living. It is true that one of the reason that Eliza wants to leave is that she wants to be independent, but it was Higgins's neglectful, unappreciated, and misunderstanding attitude that wound her heart and make her seek no reason to stay. In terms of Eliza's accepting Freddy, we know that Eliza dose not asking too much and only wants someone's "love" and someone to share feelings with her, though, unrealistic.