Profile the animal, pull all the hair on the top of her neck up. From the withers to her poll. Take a straight object (cardboard, stick, showstick) and place on her starting on her withers, and resting it on her poll. You can take some white show foam, or white touch up, and spray over the straigt object to make yourself a line on the calf. Take away the straight object. Clip off unwanted hair following the line you painted. It is much like putting tape on a wall for making straight lines when painting a room. Steirwelt does this all the time, but for the tailhead. It will REALLY help you to make a PERFECT straight line. DONT clip the hair directly behind her poll. Basically if looking at her from her side, you should clip from withers, to the top of her poll. Sorry to say it so many times in different ways, but it is REALLY important to KEEP that hair in the area directly behind their poll...usually where the halter rests. You will notise that in photos of professionally fit calves, their halters sit in quite a bit of hair behind the poll. The worst thing you could do is take that hair off the TOP of her neck off. Keep it. Also, take down the shoulders as much as possible. Someone else said to peel off the neck hair on the sides, but I would take of the shoulder hair, and pull out the neck hair and clip her entire front end like a cone.
I have attatched the most stellar drawing anyone will ever lay eyes on. Ha HA. I am by all means, joking!! I think that the drawing could help you understand a bit better though. The arrows are in the direction you should pull the hair. The straight lines are how the calf should look after being clipped. I would be nice if you had some time before your show so you could try some clipping, and then allow for grow back if it ends up being a disaster. But it shouldnt be a disaster if you take my advice (wink wink). Good Luck, and I know your heifer does not have a lot of hair, but it would REALLY help if you got rid of some of her hair in some crucial areas.