Her and St John of the Cross were good friends and fellow Carmelite reformers. They were both mystics who wrote of their experiences, considered some of the most insightful and important spiritual writings in the Catholic tradition. Both are not only saints but also doctors of the Church. In personality Teresa was more outgoing while John more reserved, at least from what I remember reading. As far as their spiritually someone more knowledgeable about their lives and writings can offer better insight than I can.
