You should clip the entire body, leaving the topline to about the width of the spine (it stops at the shoulders, clip the neck clean). Clip the head, the legs all the way down to the hooves (you will probably need smaller clippers for this). If she is deep bodied enough naturally, clip the belly, if she needs some depth then leave the hair on her belly and just trim it. Doing the topline is probably the most important thing and it takes practice. Use a blow dryer and brush to pull the topline up (the opposite way it grows). Use a spray like Clear Magic to hold it in place, then using your clippers, trim it down so it is even. The topline is a good tool to correct your heifers weak spots, if she is slightly swaybacked for example, leave more hair in the center of her back and trim the rest of it shorter so it is all even! If you have any more questions about dairy clipping or fitting you can PM me or email me, I have been showing and fitting my own dairy since I was 12.