No Aslan can't be a woman He is the most important person it the whole story he is God Jesus and the Holy Ghost the 3 in one that is the whole point CS wrote the books it the real reason the children are broght to Narnia is because by knowing him there for a short time they will hopefully know him better in our world He tells them he goes by a different name in our world and that they must learn to know him by it

If all that changes there is no reason for the story