The symptoms are suggestive of Osteoarthritis of the knee. It is an Age related damage to the knee which usually happens a lot faster in obese individuals and females after menopause.
Next Steps
She needs to get an Orthopaedic consult to see how bad the joint is. If in early stages then the joint destruction can be slowed with a combination of medicines and physiotherapy and lifestyle modifications. Later stages need a replacement surgery.
Health Tips
Avoid climbing stairs,kneeling, squatting