Siatic Nerve Damage

My mother, has worked at the Waffle House for about twenty years or so, and while workng there, she has hurt her back repeatdly…and now she has severe siatic nerve damage…and the doctors keep telling her there is now way to get rid of the pain!!!! except to make it feel better she can excersise. How can she do this when she hurts so bad she can hardly move?? Is there anything that can been done???