On the Feast of Saint Francis of Assisi, the Sephardic Doctor of the Church, I happen to come across this article which reports that Pope Francis might appoint a female cardinal. He happened to mention such action indirectly in "The Interview."
To clarify some talking points, being a Cardinal is not synonymous with the Sacrament of Holy Orders. Since only baptized men can validly receive Holy Orders, and that the Pope is Bishop of Rome, he must be consecrated a bishop before being seated on the Chair of Peter. So therefore it is not possible for a Pope Joan to appear on the loggia.
In terms of the Cardinal-electors, there are no defined requirements on who can be Cardinals. In the Pre-Reformation Renaissance, many of the Cardinals were Medici relatives who were often married and not clerics. Even 10-year-old boys became cardinals and they didn't even receive Confirmation yet! Even counts, dukes, and princes were cardinals!
Now if a woman were to become a Cardinal, she might vote, but is ineligible for the Papacy because she is not a man. But Canon Law states that any baptized man can become Pope, so that means I could have been elected.
Since there are 4 minor orders and 4 major orders of Ordination, only men can receive them, and once a man is ordained to the subdiaconate (the first major order), he traditionally takes a vow of celibacy. While the Greek Orthodox Church allows married priests, they do not allow married bishops for the same reasons the Roman Catholic Church: Jesus Christ was never married, and the Bishop possesses the fullness of the priesthood of Jesus Christ. To that end, if a married man is elected Pope, he cannot be seated because he cannot be validly consecrated a bishop.
In terms of a female cardinal, I don't see it happening. While some Mother Superiors were petitioning to have some input the last time, it will not happen as long as the Holy Ghost protects the Church. Would Sister Mary Cardinal Smith wear a red habit? Maybe for Halloween, but not in real life.