Why Does Swelling Persist In Knee Even After Various Treatment?

My 91 year old mother has swelling from her right knee all the way down to her ankle. She saw a physician over a year ago and he said she had tendinitis; however, the swelling still persists and she had an open place on her leg several months ago and water oozed out. She has wore compression hose and some ankle braces trying to reduce the swelling. In the mornings the swelling has gone down a bit but when she is on her feet for any length of time, the swelling returns. She has applied ice packs and that seems to help. I feel like there might be something else wrong because it s been over a year. What do you suggest?