What was Radhabai Deshmukh's specific goal, and what extreme measures did she take to achieve it in Shirdi?

Radhabai, the elderly mother of Khashaba Deshmukh, came to Shirdi with a singular, powerful longing in her heart: to make Sai Baba her Guru and receive a personal instruction or "secret mantra" directly from His mouth. Chapter 18 explains that she believed any mantra from another source would be "impure." To compel Baba to grant her this grace, she made a firm resolve and sat in a "dharna," renouncing all food and water. This extreme austerity, a fast unto death, lasted for three days and nights, showing the depth of her faith and determination.