I 472 was the year of the Nirnaeth Arnoediad, and after that battle Aerin's homeland of Dor-lómin was occupied by Easterlings. One of their number, Brodda, forced Aerin to become his wife, so she would probably have been born at least twenty years earlier, in (say) I 452. Some twenty-three years after the Nirnaeth, in I 495, Aerin's kinsman Túrin returned to Dor-lómin and slew Brodda. Aerin herself did not expect to survive for long after this, and probably died the same year, though we do not have a definitive account of her death.
2
The name element Aer- usually means 'sea' (as for example in Aerandir, 'Sea-wanderer'). In Aerin's case, however, neither she nor her people had any notable connection to the Sea. This suggests that some other interpretation may be intended but, if so, that interpretation remains mysterious.
3
Aerin was known to be a kinswoman of Húrin in some degree, but the only specific detail we have about her family is that her father's name was Indor. In early versions of the legends of the First Age, Indor is given as the name of Tuor's paternal grandfather (the character who would later be called Galdor). Galdor was Húrin's father, so if this relationship held, then Aerin would not merely be a kinswoman of Húrin, but actually his sister. This is hardly plausible, and rather it seems that the name Indor was transferred to another, less significant, descendant of the House of Hador.