Good question, very simple answer. Herself! It is the way she feels
about herself, her selfworth. If she's confident in herself, she'll
excude sexuality that can not be missed. Not to leave out her husband,
partner, of whatever, given the fact that females are emotional
creatures with very complex moods, her husband has a lot to do with how
sexy she views herself. She has feel loved, sexy in his eyes and
protected by him, emotionally speaking that is. For a man to cause her
emotional stress on a regular basis will tear down the confidence she
has in herself regarding how sexy she is. I'm not an expert, just my
humble opinion.