Read with intrest your question, like you i have an old lady of at least 9 years (old for a cheviot) who runs every winter for the last 4 years with the new batch of ewe lambs i keep. The "Old Lady" is all the name she has as i am finm about not naming the food, i kept her on when she threw a prolapse during lambing the first year i had sheep and at the suggesting of my sheep sensi i kept her as flock leader for the wee ones. Like your Elfie she does Boss the others leading and somewhat dominating them, importantly teaching them life away from thier mothers, how to eat hay, dry food and leading them from field to field. I would not worry about her small stature, its my experiance that small sheep grow right big elbows at feeding time and are usual experts at getting thier fair share, and anyoneselse they can bolt down quick. I suspect that Elfie has earned her place of respect from your other sheep, and that she will be your flock alpha female for a while to come.
best of luck with the new sheepies, graemscifi