The Guru Granth Sahib, her strongest attestation, records no dates for her at all. The secondary Sikh reference literature that does venture birth and death years disagrees with itself, and no independent Mughal-era or Sikh documentary record has settled the question either way. The sixteenth-century placement usually given rests on her documented contemporaneity with Guru Angad's tenure as Guru from 1539 to 1552, not on a dated record of her own life.
What would resolve this An independent contemporary or near-contemporary Sikh or Mughal-era record naming a specific year for her birth or her death would settle this. Absent that, a scholarly reconciliation of the secondary sources' disagreement, explaining which figures are more reliable and why, would at least narrow the range presently offered.
OpenSikh history and textual studiesMax Arthur Macauliffe, The Sikh Religion: Its Gurus, Sacred Writings and Authors, vol. 1