She may have a hematoma or blood clot somewhere. It kind of reminds me of something that I saw on DiscoveryHealth once. A boy was playing basketball with friends. He fell hard on his back, but got up quickly thinking the lights were just knocked out of him a bit. A few weeks later, he was unable to move at times, got stiff. He finally went in for an xray and the docs found a blood clot or hematoma that had formed near his spine where he had fallen on his back. Luckily they were able to remove it because it was causing so much pressure on his spinal column. He was never able to walk like he used to but can walk slowly.