Hello there,,,,first and foremost dont worry much,,,with ageing people do get lot of health problems ...knee joint pain is very common....but to be sure what problem she is having....you need to get herself examined by a Orthopadecian or Musculoskeletal Physio.
Depending on the severity of the condition appropriate medication,supplimentation,Electro modalities,Exercise or Intervention can be decided.
Next Steps
Get Xrays of both the knees in AP & Lat position
Do get her Blood test for ,CBC,sr
calcium,sr
uric acid,ViTD and RA factor.
Health Tips
for the timebeing avoid crossleg sitting and stair climbing activities and wear knee cap till you get professional opinion.
do get back to me if you have any furthur queries
Regards & take care.