So I did a combination of both WhoMe and goldencurly's ideas. I lay down 60 strands of black yarn (30 pieces folded) on top of a thin piece of white fusible interfacing that was maybe 5" long. I ironed the yarn onto the interfacing and it held pretty well. Then i ran a seam of black thread down he middle of the interfacing so it looked like parted hair. (I also cut the folded loops of yarn on the one side so there were 60 strands of flowing hair.)
Then i hot-glued the strip of interfacing onto the top of a white tube sock that i pulled over a styrofoam ball.
Because Susan B Anthony wore a low bun, i glued the strands of hair onto her scalp in the way hair would lie if you were wearing your hair parted in the middle and a low bun (and had no ears).
So fun. Now I want to join Pinterest and start making cloth dolls! (And I thought I hated crafts.)
She's not finished yet but here are some quick pics. I scaled back my conceptualization of it so my daughter really could help and it would look like she helped.
Thanks for the suggestions!