What Causes Sudden Inability To Walk?

Hi, first of all the question am gona ask is kinda complicated and its not about me. Its about my friend, my friend s condition. She can t walk for four years now, its not that she had accident or any spin core problems, she just stoped walking after her dead died and after her boyfriend left her the next day. She has been to doctors done all the X-ray scans , there is no sign of blood clot there or any fraction that might lead to medical invalid or paralized condition as she is right now. SO would like to hear for your answer , how can she walk again ? what should be done? Thanks in Advance..