If a woman is single and not a nidda(she went to the mikve), she is an erva only to her relatives. A nephew, a brother-in-law etc. would be included. She is forbidden to to do an a aveira(chas ve’sholom) with a non-relative also, but it is not gilui arayos. However, she is not supposed to go to the mikve.
If she is a niddah, she is an erva to all men. I am not 100% sure about how the issur of hirhur whould apply in this case.