K.W.
I had post partum edema, particularly in my legs and feet after the birth of my second child. I was told that it was the result of the epidural. I used TED stockings (compression stockings) and tried to stay off of my feet as much as possible, keeping them elevated while laying down. However, her swelling should be decreasing little by little 10 days after the birth. It sounds like there may be more to her condition than just post-partum edema. Maybe you could suggest that your sister get a second opinion, even if she starts with her own primary care physician. Sometimes, OB doctors dismiss the complaints of their pregnant/ postpartum patients, assuming that everything is just a result of the pregnancy.
Also, is it possible that your sister had pre-eclampsia during her pregnancy? I had this condition with my first pregnancy and it can cause edema, high blood pressure, and elevated liver enzymes. The "cure" for it is to deliver the baby, but it can take up to 6 weeks postpartum for everything to return to normal. Encourage your sister to ask more questions. Good luck!