Fatima of Nishapur is dated to the ninth century only through her documented circle, her marriage to Ahmad ibn Khadrawayh and her correspondence with Bayazid Bistami and Dhu'l-Nun al-Misri, both of whom rated her spiritual standing above any man they had known. No contemporary source records her actual birth or death year; her fullest biography, Attar's Tadhkirat al-Awliya, was compiled some three centuries after she lived.
What would resolve this A datable document or independent biographical notice about Fatima of Nishapur contemporary with her own life, rather than only the later hagiographical tradition and the death dates of the male contemporaries she corresponded with.
OpenHistory of early Sufism, Islamic studiesP. Bearman et al. (eds.), Encyclopaedia of Islam (Brill), 2nd and 3rd editions