What Causes Swelling In Shin Area During Warm Up?

My daughter is a distance running and is experiencing an issue with her shin. She also has scholiosis, so one leg is slightly shorter than the other. On the inside of her lower leg, when she is starting her warm up mile, there is an area about 2 inches that swells on the inside of her shin area - not on the bone, but on the muscle. After her workout, she ices it and it immediately goes away. She has been icing and doing extra stretching as well as taking a couple of days off - but it continues to return. Any advice?