Cardinals are an appointed position. A nun could be appointed Cardinal.
Where in the world do come up with such nonsense?
Canon 351 § 1 of the 1983 Code of Canon Law.
The Roman Pontiff freely selects men to be promoted as cardinals, who have been ordained at least into the order of the presbyterate and are especially outstanding in doctrine, morals, piety, and prudence in action; those who are not yet bishops must receive episcopal consecration.”