EMPLOYEE WAS HELPING TO SET UP ROCK CRUSHER. A 988B LOADER BUCKET WAS POSITIONED OVER A CONVEYOR THAT WAS ALREADY SET IN PLACE WITH TAIL SECTION ON BLOCKS. WHEN LOADER STARTED TO BACK UP, THE TOOTH ON BUCKET HOOKED CONVEYOR FORCING IT OFF BLOCKS. EMPLOYEE WAS COMING OUT FROM UNDER SCREEN TRAILER- HER LEG GOT CAUGHT BETWEEN CONVEYOR AND SCREEN TRAILER.