Lightbrite – I don’t think Sara Schnirer’s main tafkid was either being a wife or a mother. And there are women who never get married (and according to “statistics” if you believe them, it is impossible for everyone to get married) – yet they still have a tafkid in life. I am not married yet and don’t know if I ever will be, but I think I still have a tafkid in life. Even if you want to assume that I will get married eventually, I still have been single for the past many years and I don’t think that means that I haven’t had a tafkid all these years. And it is entirely possible that I will never get married, and that doesn’t mean that I have no tafkid in life.
I do agree with you that being a mother and/or wife is the most important role for a woman (I’m not sure which of the two is more important, but I do think you make an interesting point on that topic), but I just think that one has to be careful how one says such things, because not everyone gets married.
Rav Leff said that a woman’s most important tafkid is being an “Aim B’yisrael” and this can be accomplished in many ways. For example, Sara Schnirer didn’t have any children, but she was the mother of all of Am Yisrael. Anyone who is involved in Chinuch or Kiruv in any way can be considered a “mother”.
It would be harder to say that there is any way to be a wife without being married, so I like Rav Leff’s vort because it can apply to anyone.