Kate responds with both weariness and defeat.  Kate, of course, has just given Helen a sweet so that (even though Helen has just stabbed Annie) Helen will drop the sewing card (which was Annie's original request).  Kate's actual reply is very telling:

ANNIE:  Why does she get a reward?  For stabbing me?

KATE:  Well-- (Then, tiredly) We catch our flies with honey, I'm afraid.  We haven't the heart for much else, and so many times she simply cannot be compelled.  (52)

Kate feels tired and defeated.  Even though she knows this might not be the right thing to teach Helen, Kate's actions evoke an easier immediate response from Helen.  This reminds me so much of the typical mistake of a toddler's mother:  to give in to the very first tantrum.  The child then learns that he or she gets what is desired by behaving poorly.  More tantrums are, of course, to come; however, at the time, appeasing the child is vastly easier.  Granted, Kate's intent here was not to reward Helen for hurting Annie.  Kate's intent was to have Helen comply in releasing the sewing card; however, the reward for injury is also an unwelcome result that Annie recognizes.