Your sister had a very serious injury to the upper part of her neck. Similar injuries have been known to kill many victims. Since she is able to walk on her own and do things by her self, the doctors have performed operations with good results. The reason her body is still partially paralysed may be that the spinal cord was irreparably damaged to that extent. Surgery has reversed those abnormalities that followed pressure on the spinal cord. The permanent damage done to the spinal cord at the time of impact will leave behind residual abnormalities despite all treatment.