My Wife Is Experiencing Pain And Some Swelling Around Her

My wife is experiencing pain and some swelling around her knee and into the top of her shin and calf area. There is redness and the area around her knee is tender to the touch. The pain seems to worsen for no reason at all and her joint is stiff. She is 5'4" and weighs 120 pounds. There has not been any trauma or blunt force to her knee. She has been complaining of throbbing pain and at times cannot put her weight down on her leg.