With what arguments does lady reason seems the intelligence of women ?

Lady Reason is one of the three virtues used by Christine de Pizan in her book "The Book of the City of Ladies". All these virtues are allegories she developed in order to build the city.  The "city" here refers to a woman's self-worth. 

Lady Reason is the first virtue she built as the external walls of the city which answers her question about why some men slander women. She tells Christine to take the spade of her intelligence and dig deep into her thoughts in order to make hods of the earth. These hods come from the past beliefs she held. Through reason, no men will look at women as weaklings and irrational who are slaves of their own emotions and incapable of rational thoughts. This virtue does not only help her dispel the negative thoughts she held about herself but also develop her self-consciousness of the greatest truth, that women are not useless creatures but as important and as rational as men. 

She was one of the world's first female heads of state.