If she gets up and abandons it, the best thing you can do for it is put it in an incubator if you have one. If you don't and you want to try to save it, you might try putting it under a heat lamp. Try to adjust the heat lamp so the temperature on the egg is about 99.5 degrees. Too hot and it will die, too cold and it will also die, so try to use a thermometer to get it right. Also try to keep the area around it moist so that it doesn't get shrinkwrapped. Maybe put it in a bin or tub with wet sponges or paper towels to try to get the humidity up. Then just wait and see. Of course, hens usually will sit on the nest a day or two after the first chicks hatch for exactly this reason, so you probably don't have much to worry about!