In the story, Ratan felt abandoned by her employer. His nonchalant rejection of her, based on his decision to return to Calcutta alone, essentially crushed her spirits.
Ratan had always been a faithful servant girl, and in her naivety, assumed that the postmaster would value and welcome her presence in his new life. As an unmarried man, Ratan's employer probably felt uncomfortable with the prospect of returning to Calcutta with a little girl in tow. The damage to his reputation might have been devastating; his chances for future material advancement and marriage prospects might have suffered. Essentially, the postmaster wasn't courageous enough to take any chances.
Because he neglected to consider matters from Ratan's point of view, the postmaster acted insensitively towards his young servant. Essentially, her faithfulness and solicitude were rewarded by abandonment and rejection. Ratan is crushed because she was loyal to and trusted the postmaster implicitly but is betrayed.