I have a limping chicken checklist of things I look for.
1. Bumblefoot or other injury to the bottom of the foot.
2. Noticeable injury to the leg. I just give a quick feel to make sure it doesn't seem like a broken bone or anything out of place.
If I don't see anything during either of those checks, I usually give the chicken a soak in a warm bath (I have a little plastic dishpan I use) with Epsom salts. Try to get them to stay in for at least 10 minutes, longer if they will tolerate it.
I don't isolate them unless the limp is really bad and I don't want them moving at all. Otherwise, I will return them to the flock and keep a close eye on her over the next days to see if it's improving.
And if someone seems like they are in a lot of pain, I will give 1/4 of a low-dose aspirin - ONLY after I have confirmed there is no bleeding, including any signs of bruising which indicate some internal bleeding. But I always assume they can pull a muscle just like we can, so sometimes a little pain relief is all it takes to get them over the hump and on to healing.