Iguana Leg Problems

Hello, 3 days ago I purchased a young green iguana from a Mexican flea market. I know that I bought her under less-than-ideal circumstances so I understand that she may have an incurable condition. Regardless, I'd like to give her a good life no matter how short. I've done some research on iguanas, but not a lot. When I first saw her she was alert, although stoic while I was holding her. I bought the terrarium that she was housed in with another iguana & I know it's too small for her. She is about 6-7’ head to vent &the tank is 10gal. I'm going to upgrade her abode soon. I got her home, fed her, gave her water, & put her to bed. The next day I gave her to a friend to hold & he put her back in her cage while I wasn't around, didn’t mention a problem. I went out of the house for a few & when I got back I noticed that she was holding her left rear leg limp. I felt it & noticed that it was slightly swollen & it was tender. I gave her a branch for her to perch on. She stayed on it all night long, but her left rear leg hung limp the whole time. The next morning I saw that it looked even more swollen. She is shedding so I checked to see if skin was cutting off her circulation, but it wasn’t. That day my friends & I had an 8-hour drive back home. She basked in the back window, her color looked fantastic, she drank water, & her appetite had improved! Today she looks good as well, but I haven't found any poop & her leg is still swollen (maybe very slightly less swollen) & she still holds it limp. I gave her a good soak this evening to get some of the dead skin off of her. I make sure that her daytime temp is around 86-95F & I misted her three times today, to moisturize her skin. She's so sweet & calm that sometimes that I wonder if she is sick. Then she will perk up. Should I be worried about her leg? MBD? Injury? What about not finding any poop? Also, I live & work on a farm with an organic garden with many veggies, but all she wants to eat is leaf lettuce! Thanks so much!