I was thinking recently again, "What is a childfree, pagan woman to do about the Mother stage of Maiden/Mother/Crone?"
One thing I just realized is that part of it is growing up enough to be in charge of your own life. I don't know if this part is as relevant, considering that the Maiden is already supposed to be independent. Maybe you even need that trait to become a Maiden, even before you become a Mother/Lover.
More relating to the "mother" part itself, I'm also realizing it is having a cup full enough to share with others. You need to reach a certain point in maturity to take care of yourself enough so that you can take care of others. And taking care of others, or self-sacrificing, needs to be willing and heartfelt. Taking care of others because you feel obligated to or because you're "supposed" to is counterproductive and harmful. A good mother gives selflessly but within reason, and only makes a truly tremendous sacrifice if it is really necessary - and with complete willingness, because of the value she realizes her sacrifice to have.