Almost perfect form. The girl needs to keep her shoulders back even more. She also needs to look up at about a 45 degree angle the whole time. Also, before you start the motion, you need to exhale all the air in your lungs, squeeze your abdonimal muscles, inhale while your abs are still squeezed, then lift. This will protect your spine more.
edit:
Also, i don't think Mark explained this, but this is mostly a 'pushing motion' with your lower body. The mistake i made when i first did this was i thought it was mostly a pulling motion with my lower back which strained my back a lot... the only 'pull' you should be doing is with your traps/shoulders to make sure you keep a slight arc in your back to protect your spine. Push off with the heels of your feet, when the bar gets past your knees, you push forward with your butt/hamstrings --- you do NOT pull with your lower back.
Also, keep your toes at a 45 degree angle.
Edit 2: Also, your arms should be like 'cables' holding the bar. you should not be using any arm strength to move the bar forward or backward...