No. Mother Teresa expressed a strong desire right from her early age to give up marriage and serve God as a nun.
Nun's take three vows; poverty, chastity and obedience. They donate all their time, talents, resources to serving in the Church and pray, and have love for God. Out of this love, God sends nuns to serve in the World.
She first became a Loreto Sister, teaching in schools. She then founded a new religious order in India, called the Missionaries of Charity. There, Mother Teresa and her nuns served Jesus in the poorest of the poor.