We are all mothers when we nurture anything, from people we mentor and support to our creativity to pets to gardens!
I very much agree. I also have chosen not to have children, but I still find myself in the mother role often. I also agree that we need to maintain a balance of all three faces within ourselves. I think each face resides in us all and we achieve a balance in that way.
I think that we don't necessarily only realize these stages on a chronological/physical level. But that there are aspects of life in which we may cycle through the stages many times.
An example that comes to mind for me personally is teaching. I begain in the Maiden stage as a student, learning the basics and working through my beginnings. Currently I am a teacher of those same basics, which I feel is a sort of Mother role. And in some areas, I am looked upon with some feeling of expertise or wisdom ( which is still a very strange thing for me)which I consider Crone traits.