What Causes Reddish Bruise Under The Arm Of A Child?

My 12 year old daughter fell on the ice and severely bruised her right elbow by falling on the ice about a week ago. Bruise got red, blue, purple like normal, but now has a noticeable slightly raised 2-3mm white spot with approx size of half dollar on a baseball size bruise. She is a tough kid and says it does not hurt, but feels different when she bends with movement. Bruise is located on under forearm, not the elbow. Any thoughts would be appreciated.