tatra tāṃ pravaṇāmeva mātaraṃ kṣaumavāsinīm| vāgyatāṃ devatāgāre dadarśā''yācatīṃ śriyam
There he beheld his mother in silk apparel engrossed in silent prayer (to the gods) for his royal fortune in the room meant for the worship of the gods.
— M.N. Dutt (1891)
Kausalya sits in silk, absorbed in silent prayer for her son's fortune. She already knows — a mother's intuition. She is not celebrating but meditating, preparing herself for the change that is coming. Her prayer is a shield around Rama that he will soon need.