DD is almost ready for new pitch (she is LHP; 1st yr of HS), has FB, good CU, curve, & drop - effective in that order. HS coach is anxious for her to have screwball- which DD does not throw, and would not likely learn next as SB has tendency to reinforce bad mechanics, but coach does not seem to accept this rationale. How necessary is it for DD to have SB?? Would like ammunition for argument (or reason to learn)