Do you have any used 2X6's or 2X8's? You need a ramp no more than 24 " wide and you must put cleats on it so the gilt will not slip. If they slip once you are in for a lot of trouble because they will not try again. Two hog panels, one on each side, wired across the 2 by's and supported at the top will make a satisfactory ramp. Also, some straw or hay scattered on the ramp along with some treat (ear of corn, slices of apple, etc) will give them a sense of security. It is so much easier if she will walk up into your truck. Ramp needs to be 6 feet long minimum. Plywood needs to be braced for a 200 pounder. even 3/4" will sag with that much weight.
Do you have a stock rack or sides on your truck? You will need something at least 4 feet above the floor of the bed or she may try to go over. Put something on the floor if it is slick to give some footing. She needs to have good footing if you are taking her to butcher so the meat will not be bruised, and if she is for raising pigs she doesn't need to be slipping on the trip home.
Good Luck! It can be as easy as pie or an experience from hell. Try not to get excited and you will have much better luck. Hope whomever has been feeding her will be there for the loading. Dave