If she is limping, does she use the leg at all? If it is a ligament, she will be unable to use that leg, but the lower leg will kind of flop around. Look to see if she has bumble foot, which is a swelling of the foot ( a type of staph infection). You need to treat with antibiotics. Likely if she has drunk from standing outside water, she may have picked up a different type of staph infection. Staph is in the soil everywhere, and for some reason poultry will sometimes pick this up. Look up on the internet staphylococcus aureus infection in poultry. You need to start treatment right away or you may lose the bird. I have lost some to this anyway and others have recovered. During rainy season, this is always something I look for in my birds since they do roam and have access to standing pools of water. Some will drink pooled dirty water and be just fine. There are all kinds of things that can cause lameness but my vote is a staph infection. I don't have a link to where I got this, but here is an excerpt:
"staphylococcus aureus is soil-borne and outbreaks in flocks often occur after storms when birds on range drink from stagnant rain pools". It can be treated. "Erythromycin and penicillin can be administered in the water for 3-5 days or in the feed for 5 days. Other antibiotics and drugs are only occasionally effective".
Ugh. Now one of *my* chickens is limping. I saw your comment on a thread about this. The hen is half a year old and otherwise looks healthy, but she's limping around (sometimes gingerly using leg but mostly hopping). The two young ones are pretty adventurous and have room to roam and jump around, so an injury seems more likely than an infection (though I do have a bag of chook tetracycline around). She's not getting picked on though I'll probably need to shoo away the other two while she's eating. You mentioned dislocated ligaments. How/where do you feel for this? In probing around, I didn't feel anything notable.