Sports Taping- stretch the tape from both ends and apply on the affected area Contrast Fomentation (Hot and Cold).

need full details and evaluation

it seems to be a degenerative osteoarthritis,which reoccurs because of lack of precautions or overuse.there can be an increase in blood uric acid level which aggravates the condition.first you should get the X-RAY one and test of Blood uric acid level done.

You need to do x ray to cinfirm severity level. Start hot application 2-3 times in a day then stretching followed by strenthing exercise. This will reduce her pain and progression.

Get an x Ray done in standing position. It seems degenerative arthritis if one looks at your mother's age. But severity and further treatment to be guided by symptoms and xray. Always remember that tkr or surgery is not the only solution.  orthopaedic or physio can help in many other ways.

Pain relief : both hot and cold fermentation 3times a day, (ice pack is much effective) ultrasound therapy and IFT can reduce the pain - consult a physiotherapist. She need to strengthen her muscles. 1) Lie flat on back and press the downwards if needed place a pillow under knee -  30 to  50 repetitions per day. 2) sit comfortably in a chair and move the leg inwards and upwards for 10 to 15 mins twice daily These two exercises you can find in Internet STATIC QUADRICEPS EXERCISES AND DYNAMIC QUADRICEPS EXERCISES or isometric exercises. 3) walking and cycling are best exercises. Walking -  1/2 a km in a day and gradually increase Cycling (static cycle) -  10 to 15 mins in a day Precautions : avoid stair climbing, avoid squatting, always sit in a chair or a stool, avoid cross leg sitting. Consult an orthopaedic doctor and take an x-ray. By seeing how much damage is there and if the pain is very severe he will advise you for the further treatment.

Arthritis can be diagnosed by various investigations X-ray, Physical examinations, and Blood tests(SGPTOT, RA factor etc...) , depending on the condition of her joints some strengthening exercises may do along with some medication that are believed to help in lubrication of the joint , or she might need a joint replacement. for both the things initial strengthening is advisable.

Looks like your mother pain is from degenerative osteoarthritis of the knee. This typically has flare ups with with varying intensity and duration of pain. Plain Xray/Radiographs of the knee in standing position in both planes can easily show the severity / stage of osteoarthritis.