Lasix not helping with edema!

Hi, my aunt is 75 years old, 150lbs, diabetic and a recent survivor of breast cancer. Both legs below the knees have been swollen for about 5 months. Took her to the doctor who sent her for a test to see if it was a bloodclot but that was ruled out so he put her on lasix and it did help a little with the swelling at first but not completely. She keeps her leg elevated above her heart for about an hour per day and moves around a little during the day. Her leg is double the size it was if that gives any help on how bad the edema is. I believe a kidney function test was also normal. Any suggestions on what she should do? Would compression socks help?