Your sex does define you to an extent, though. Whether or not you decide to have children you will be defined by the fact that if you do, or don't, it is you who will become pregnant and give birth.......and if you do give birth, it will impact upon you, and change you, in ways it doesn't impact upon or change the father of the child. If you don't ,or can't, have children you will still be aware of the ticking of the biological clock...and have to rationalise that experience/your choices/limitations in order to make meaning of your life.
How you deal with the inevitable stereotyping due to your sex will also define you; which bits of 'femininity' ( if any) you align with, and which you don't; and how you to choose to respond to certain expectations or reject them.
I don't think any of us can claim that we are entirely separate from our body, from the facts of that body; that our body does not define us in certain ways; or certainly shape us and our way of navigating the world.