Semenya is a woman only if we decide that each person decides what he or she is. There are men, women, pre-op trannies, post-op trannies, hermaphrodites, androgenites, high testosterone women and low testosterone men. In society, you can pretty much be whatever you define yourself to be. Hell, Hemingway's son went through most of his adult life sometimes as Gregory, a man, and sometimes as Gloria, a woman. He did not change one for the other -- he used both.
But in sports we simply can't let people decide what gender they want to be. Semenya clearly has more testosterone than she should have to be running against women. It is not her fault, and the IAAF supposedly "required" her to undergo hormone treatments to bring her estrogen up and her testosterone down. Whether she did the treatments or not was apparently left up to her. If she did them they appear to have had little effect.
Semenya and any other "woman" with her level of testosterone and muscle mass should not be in a women's race.