The Collaborative International Dictionary of English v.0.48:

Sempstress \Semp"stress\, n.
   A seamstress.
   [1913 Webster]

         Two hundred sepstress were employed to make me shirts.
                                                  --Swift.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sempstress
    n 1: someone who makes or mends dresses [syn: dressmaker,
         modiste, needlewoman, seamstress, sempstress]