redhack,any repetitive motion can cause injury,typing on your keyboard all day can cause injury.slugger is right,conditioning and stamina might allow your dd to pitch longer,but that doesn't mean that after a while that injury won't occur because of over use.
I think the lack of distinction between "injury" and "wear and tear" is disappointing. Golf swings, tennis, free throws, running all can cause wear and tear, and injuries for over use.
I wonder what the "injury" rate is on a drivers accelerator foot for driving 2 hours per day for 20 years.
I worry more about catchers that will not be walking in 20 years from now. Its not from injuries either.