It appears that in His transcendental ecstasy, Śrī Caitanya Mahāprabhu forgot to eat for three continuous days. He was then misled by Nityānanda Prabhu, who said that the river Ganges was the Yamunā. Because the Lord was in the ecstasy of going to Vṛndāvana, He was engladdened to see the Yamunā, although in actuality the river was the Ganges. In this way the Lord was brought to the house of Advaita Prabhu at Śāntipura after three days, and He accepted food there. As long as the Lord remained there, He saw His mother,Śacīdevī, and every night executed congregational chanting with all the devotees.
(Sri Caitanya Caritamrta----2:1:94----purport).

Śrī Caitanya Mahāprabhu knew very well that His acceptance of sannyāsa was a thunderbolt for His mother. He therefore called for His mother and the devotees from Māyāpura, and by the arrangement of Śrī Advaita Ācārya, He met them for the last time after His acceptance of sannyāsa. His mother was overwhelmed with grief when she saw that He was clean-shaven. There was no longer any beautiful hair on His head. Mother Śacī was pacified by all the devotees, and Lord Caitanya Mahāprabhu asked her to cook for Him because He was very hungry, not having taken anything for three days.
(Sri Caitanya Caritamrta----2:1:95----purport).

In his Amṛta-pravāha-bhāṣya, Śrīla Bhaktivinoda Ṭhākura gives the following summary of the Third Chapter. After accepting the sannyāsa order at Katwa, Śrī Caitanya Mahāprabhu traveled continuously for three days in Rāḍha-deśa and, by the trick of Nityānanda Prabhu, eventually came to the western side of Śāntipura. Śrī Caitanya Mahāprabhu was induced to believe that the river Ganges was the Yamunā. When He was worshiping the sacred river, Advaita Prabhu arrived in a boat. Advaita Prabhu asked Him to take His bath in the Ganges and took Him to His (Advaita's) house. There all the Navadvīpa devotees, along with mother Śacīdevī, came to see Śrī Caitanya Mahāprabhu. This house was located at Śāntipura. Mother Śacīdevī cooked for Śrī Caitanya Mahāprabhu and Nityānanda Prabhu, and at that time there were many joking exchanges between Advaita Prabhu and Nityānanda Prabhu. In the evening there was a mass saṅkīrtana at the house of Advaita Prabhu, and mother Śacīdevī gave Śrī Caitanya Mahāprabhu permission to leave. She requested Him to make Jagannātha Purī, Nīlācala, His headquarters. Śrī Caitanya Mahāprabhu granted His mother's request and, followed by Nityānanda, Mukunda, Jagadānanda and Dāmodara, left Śāntipura. Bidding farewell to mother Śacīdevī, they all proceeded toward Jagannātha Purī, following the path of Chatrabhoga.
(Sri Caitanya Caritamrta----2:3--summary).

These verses indicate that mother Śacī, born in the family of Nīlāmbara Cakravartī, used to worship Lord Viṣṇu even before her marriage. As stated in the Bhagavad-gītā (6.41):
prāpya puṇya-kṛtāṁ lokān uṣitvā śāśvatīḥ samāḥ
śucīnāṁ śrīmatāṁ gehe yoga-bhraṣṭo ’bhijāyate
"The unsuccessful yogī, after many, many years of enjoyment on the planets of the pious living entities, is born into a family of righteous people, or into a family of rich aristocracy." MotherŚacī, a nitya-siddha living entity, is an incarnation of mother Yaśodā. She appeared in the house of Nīlāmbara Cakravartī and was everlastingly engaged in the service of Lord Viṣṇu. Later she directly had as her child Lord Viṣṇu, Śrī Caitanya Mahāprabhu, and she served Him from the day of His appearance.
(Sri Caitanya Caritamrta----2:3:167----purport).

It is a great happiness for a mother if her son does not leave home to search out Kṛṣṇa but remains with her. At the same time, if a son does not search after Kṛṣṇa but simply remains at home, he is certainly blamed by experienced saintly persons. Such blame certainly causes great unhappiness for a mother. If a real mother wants her son to progress spiritually, she had better allow him to go out searching for Kṛṣṇa. The mother naturally desires the welfare of the son. If a mother does not allow her son to search for Kṛṣṇa, she is called mā, which indicates māyā. By allowing her son to go as a sannyāsī and search for Kṛṣṇa, Śacīmātā instructs all mothers of the world. She indicates that all sons should become real devotees of Kṛṣṇa and should not stay at home under the care of an affectionate mother.
(Sri Caitanya Caritamrta----2:3:181----purport).

To stop the cycle of birth and death, one has to understand Kṛṣṇa as He is. Simply by knowing Kṛṣṇa, one can stop the process of rebirth into this material world. By acting in Kṛṣṇa consciousness, one can return to Godhead. The highest perfection of life is for a father, mother, spiritual master, husband or any other family member to help others return home, back to Godhead. That is the most preferred welfare activity for the benefit of relatives. Therefore, Śacīmātā, although the mother of Nimāi Paṇḍita, Śrī Caitanya Mahāprabhu, considered all the facts and decided to allow her son to go out and search for Kṛṣṇa. At the same time, she made some arrangements in order that she might get news of all the activities of Śrī Caitanya Mahāprabhu.
(Sri Caitanya Caritamrta----2:3:181----purport).