As you hv mentioned that she is suffering from a long time, it may be Osteoarthritis or Rheumatoid arthritis. You need to get her examined and diagnosed for proper treatment. Ayurveda surely gives good relief in all joint conditions.
Next Steps
Consult directly to treat your condition.
Health Tips
Try applying Arthorub liniment and dry fomentation with Hot water bag at bedtime. Using Knee caps may give support to knees while walking.