For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
Henry Higgins bets Colonel Pickering that he can turn Eliza Doolittle, a flower girl, into a duchess in six months. After dealing with her for a short while, they both agree it will be a tough task.
Act II
After successfully "passing off" the flower girl as a duchess, Higgins wins the bet, but Eliza is left angry and dissatisfied.
Act III
Eliza runs away from Higgins; they meet again and argue once more before she says goodbye for what she thinks is the last time. Higgins thinks otherwise.