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
Christine de Pizan sits down one day and reads a wretched book about how horrible women are. She is so saddened by the book (huh, wonder why?) that she bemoans the fact that she was born a woman.
Just when things look totally bleak, though, she's visited by three magical ladies whose names are Reason, Rectitude, and Justice. No, The Book of the City of Ladies is not long on subtlety.
These ladies inform her that in the eyes of God, women are just as good as men. And to give women a place where they can thrive, the ladies instruct Christine to build a City of Ladies. Christine gets to work right away, and while building the city, she chats with each of the three ladies.
Act II
Christine's conversations with the three ladies all go the same way. Christine will mention a common stereotype that men use to insult women, then one of the three ladies will show her why this argument is so wrong.
The ladies are especially fond of using so many examples of great women to show how wrong men are for insulting women so much. Eventually, we get the sense that we're reading The Encyclopedia of Great Women from History and Literature. Which makes sense when you think about it, since Christine de Pizan wants her City of Ladies to be populated by only the best and brightest women.
Act III
Once Christine has finished building the City of Ladies, Lady Justice helps her fill it with all of the best women from history and literature. Things are looking really excellently feminist.
In the end, Christine makes a complete 180 and encourages all women to be humble, moral, and—most of all—obedient to their husbands. This sudden emphasis on obedience is strange, but Christine no doubt uses it strategically so many of her male readers will be more inclined to agree with her earlier arguments about women's goodness.
Also, this was 1405 and women's rights were very much not a thing. de Pizan was probably trying to stay out of trouble, so she topped this progressive literary sundae with an antiquated The Taming of The Shrew-type maraschino cherry ending.