I studied exercise science in college, so this topic was often a big issue. Women differ greatly from men. Men's bodies don't need fat to function; they can have as low as 2% body fat and be fine. Women, on the other hand, need a certain amount of body fat to remain healthy. Women should have a minimum of 10-13% body fat, and that is for the extreme athlete bare minimum percentage. The athletic woman should still be between 14-18% and the average woman should be between 19-24%.
In summary, the ideal percentage for a woman is probably between 16-22%.