nienor

A girl who don't bother to check the adoption records and accidentally marries her bro. Also applies if said girl sleeps with him without checking (aka "elvish marriage"). She may get depression or commit suicide upon discovery of the ugly truth.

My friend was such a Nienor! She just found out from the records that her husband of three years is her brother. She didn't even bother to check before she decided to marry him!