What Causes Numbness In The Legs?

My sister has complete numbness from her legs up she cannot stand she only feels pressure that lets get know that she has to use the bathroom..she has been tested for Lyme disease,als, gulliam Bart syndrome, she is not diabetic nor does she have hpb,thyroid tests negative, she was released from the hospital with directions to take prednisone and neurontin,which the doctors think it could be viral.my family is at a loss as to what she has she has no reflexes in her arms,hands,knees. Do you have any suggestions