M. Teresa had the determination of a terrier, and chps 4-6 illustrate this over and over in the book Come Be My Light.
Here’s the big picture. M. Teresa, to fulfill the mystical vision she got from Jesus about forming the Missionaries of Charity for the poorest of poor in Calcutta, had to get permissions at various levels:

Her vow as a Loreto sister had to be annulled since it was conventual.
Her spiritual director had to give her permission.
The Archbishop of India had to give her permission.
The Pope, or Rome, had to give her permission.
When she first told her director, Fr. Van Exem, he told her to keep the idea to herself for months. Then she was given permission to work with the Archbishop, a certain Perier. The latter simply wanted time to gain clarity of her motive and the will of God. He deliberated for a long, long time — about a year. Then Rome was slow and then she was saddled with some criticisms and some envy and some politics and it took a long, long time for her to have a vision and to establish a ministry.
The determination of M. Teresa is a powerful testimony of her will, her confidence in the vision, and her commitment not to let go until God had gained the upper hand. Her determination reflects her faith.
“Day after day,” she writes to the Archbishop, “hour after hour, He asks the same question: “Wilt thou refuse to do this for Me?” I tell Him that the answer is with you” (66).
The Archbishop both knew the power was in his hands and he knew as well that he had to discern God’s will for the missionary work in Calcutta. The time of testing drew out of M. Teresa clarity as to what the Missionaries of Charity would do: essentially they would sell out for God, their fires would burn for the missionary work to the poor, they would totally depend on God and identify with the poor.
Involved in this time of testing were some potent experiences of union with Christ. I think these times of union also influenced her perception of darkness: “There [where she was then residing] as if Our Lord just gave Himself to me — to the full. The sweetness & consolation & union of those 6 months passed but too soon” (83).
She speaks of a three-fold vision of being summoned by Jesus and the crowd of the poor to “Come,” of Mary’s words for her to “Bring them to Jesus — carry Jesus to them,” and a vision of darkness enveloping the crowd and words from Jesus and Mary to go to the crowd. “Will you refuse to do this for me?”
Once she gained approval, however, there were still challenges and tests. She got final permission from Rome on August 8, 1948. 9 days later, August 17, 1948, “clad in a white sari with a blue border, Mother Teresa … set out to begin a life as a Missionary of “Charity” (121). She chose to leave with just five rupees