There could be many things causing swelling in the legs and unless you had xrays, blood work and the entire gambit of tests, you may never know.
She might have some bacterial infection somewhere in the body settling in the legs. You could try some antibacterial meds on her for a while. Something that does not actually kill the bacteria but don't allow it to reproduce. These types of meds are easier on the bird and are less toxic. These meds keep the bacteria at bay while the bird's immune system heals the bird.
So something like Doxycycline or Amoxicillin. In this case, I think the Doxy would be better to use and it works better on internal tissues, where as the Amox is great for respiratory ailments. You can get both of these on line from pet supply, even fish supply places. All the same stuff. Human grade is exactly the same as well.
Try the Doxy out for about 2 weeks and see if it makes any difference in the swelling. Of course if at anytime she looks like it is making her worse, then stop all together. I doubt this stuff will cause her to worsen, but we don't know if she does have an infection at all.
If she does start to respond, keep her on it for another 2 weeks and see how it goes. (I know it sounds like a long time for antibacterial meds, but sometimes long term medicating is necessary even in humans with bad infections)
When you are done with any treatment, offer up probiotics in the water for 1 week following treatment to replace all good bacteria that was lost.
You might also try boosting up the immune system with lots of healthy veggies and fruits, greens, meal worms, etc...Natural things that can not be gotten from gamebird food. Sometimes these sort of ailments are stemming from a weak immune system.
I hope she makes a full recovery.
