Knee cap pain. Pain has been increased.

If it's a sudden gradual increase in pain in the last few days it could be either a condition called chondromalacia patella which involves the under surface of the patella. Pain during climbing up or down the stairs, pain while getting up from a chair or pain during squatting are the usual symptoms. This pain is usually not seen during walking but only during the above mentioned activities unless it is too severe. The other condition which fits your mom's symptom picture is the age related Osteoarthritis. Chronic pain for several months during walking is indicative of Primary Osteoarthritis which may be progressive unless treated at detection. Acute pain could be due to exacerbation of a chronic condition or strain of the muscles around the joint due to  unaccustomed activities. This is a brief idea, however, there are a few other conditions which could cause knee cap pains in that age group.

Orthopaedic consultation along with and X-ray of the Knee -AP, lateral and Skyline views are required. MR Cartogram maybe required in case of a cartilage related problem

Avoid activities causing pain. Start Isometric knee strengthening exercises