I do not know Apple's worker demographic. But at college level, we see wide variations. In CS majors, females only represent about 20% of the student population. Provided that female are also more likely socially to be the one to sacrifice their career for their family, it might be VERY hard to get to over 35% of female worker in your software business.
The issue with diversity in CS is not a college level problem. Only few female student register for the class and they do not really come to information sessions about the program. Overall, I'd say the root cause is much before college. It is in the gender stereotypes. I was in Barnes and Nobles last week and passed by the children's book section. One side was labeled boys books and had books about trains, cars and plane. The other was labeled girls books and was about princesses, fashion and poneys.