Character Analysis
Once Christine de Pizan has finished constructing the City of Ladies, she decides to give it a ruler, so she recruits the Queen of Heaven to fill that role. This is most likely a compromise that Christine makes. Earlier in the book she talks about the all-female culture of the Amazons, which elected its leaders democratically. Christine clearly likes this sort of society, but being a person who lived under the monarchy of medieval France, she didn't want to put her neck on the proverbial chopping block by criticizing the system of government.
So in the end, the City of Ladies gets a female ruler in the Queen of Heaven. We don't see her for very long, but she seems cool enough when she says,
"O Justice, greatly beloved by my son, I will live and abide most happily among my sisters and friends, for Reason, Rectitude, and you, as well as Nature, urge me to do so. They serve, praise, and honor me unceasingly, for I am and will always be the head of the feminine sex." (3.1.3)
The son that's mentioned here is probably Jesus Christ, meaning that the Queen of Heaven is none other than the Virgin Mary, who Christine de Pizan has praised many times throughout this book. All in all, the mother of Jesus Christ is a pretty decent choice for queen. Could have done a lot worse, de Pizan.