Is there help for unstable gait/poor balance.

I am writing on behalf of my 77-year old mother.  In 1994, she had a triple arthrodesis of her left foot and ankle.  In 1995, she had a total knee replacement of her right knee.  In August 2005, she unknowingly suffered a fracture of her right fibula above the ankle joint and walked on it for three months.  She was fitted with a foot and ankle brace until the bone healed.  In May 2006, she underwent a total knee replacement of her left knee with the left foot being abducted to 50 degrees.  In August 2007, she underwent a revision of the left knee replacement to correct the angle of the left foot to 15 degrees.  Since that time, she has had a seriously unsteady gait and is unable to walk without a walker.  Please advise if there is some procedure which might correct or lessen her gait problem; she is essentially an invalid at this point.