In the Osiris myth, the goddess who helped Isis search for Osiris’s body and mourned him was Nephthys.
Nephthys was the sister of Isis and the wife of Seth in the traditional family genealogy. After Seth killed Osiris, Nephthys joined Isis in mourning and in the search for the dismembered god. Their partnership made both goddesses important protectors of the dead and of the burial process.
Nephthys is sometimes overlooked because Isis has the more prominent role in the story. Yet Egyptian funerary art frequently paired the sisters. Nephthys could stand at the head of the coffin while Isis stood at the foot, together guarding the deceased.
Her connection with Anubis is also important. In some traditions, Nephthys was identified as Anubis’s mother, although Egyptian genealogies vary by period and source. This variation is why a single family tree should not be treated as universal across all Egyptian history.