She might be having synovitis ( inflammation of joint lining) which may be due to degeneration, metabolic abnormalities ( uric acid ) or even infection. Please bring her to hospital for a clinical examination to ascertain the cause of her knee pain. Till then apply any gel or spray

Is there any fever?if there is fever, then it could be septic arthritis.Take the patient to a hospital. This treatment is being suggested on bases of the information provided. However I would like to examine & investigate the patient  in detail. Control  Hypertension, Diabetes or any other metabolic disorder. if there is  any. Any way it may be tried, --. Dolokind Plus (Mankind) [Aceclofenac100 mg +Paracetamol 350 mg] 1 tab. OD & SOS. X 5 days. --. Caldikind plus  (Mankind) 1 tab OD x 10 days. (You may need help of your local doctor to get these medicines.) --. Fomentation with warm water. Let the part not be exposed to cold air. --. Sleep on a hard bed with soft bedding. --. Use no pillow under the head. --. Avoid painful acts & activities. -- .Do mild exercises for knees and ankles. --.(Take help of a  physiotherapist). --Do not ignore, let it not become beginning of a major problem. --Do ask for a detailed treatment plan. Kindly make sure, there is no allergy to any of these medicines. --For emergency treatment visit nearest hospital. --Wish you a quick recovery & good health. --I hope, I have solved your problem to your satisfaction.  Dr N C Gupta MS (ortho)

Arthritis..

Since there is swelling arthritis is a possibility Pl consult through practo pro

Most likely due to degenerative changes in the knee. Need to see a recent X-ray of the knees with online consult