Ok, so you've almost had her for six months. She's likely to have a heavy parasite load. It's time to worm her and treat her for external parasites. There are many products that you can use. You can put a wormer called Moxidectin in the drinking water and that will treat both internal and external parasites. You need to retreat after 10-14 days. There are other wormers that will do intestinal worms, which are available from your local product store or vet. If you use something that doesn't cover lice and mites, then you will also need to dust her with an insecticidal powder like Pestene or Derris dust. There is a lot of information about worms and worming in the A-Z sticky at the top of the Good Sammy section.
Laying pellets are a good diet for a laying bird. Try to keep the laying pellets to 80% of her diet so she only being supplemented with kitchen scraps as treats. When feeding grass, long strands can cause a problem in the crop. It's best for chickens to be able to range on grass and peck the grass themselves. If you throw grass over, make sure that it's short grass. The shell grit is good.
I'm assuming that when you cleaned the foot in water that you looked over it carefully. I hope there was no swelling or little scabs in the foot pad area. Did you check over the leg as well as the foot to see if there are any injuries? If there is, then get back to us.
I think it's most likely that your chicken has jumped off the perch and landed awkwardly, or sprained the leg in some way. How high are the perches? Sprains can happen and if that's the case it will gradually get better. Another possibility is that she has developed a nutritional deficiency, although the diet you are giving her sounds quite okay. If you want to be sure about that you could boost her diet for a few weeks by putting her on the rickets diet. Rickets is a condition that birds develop particularly when they are growing if they aren't getting the right nutrients. It can show up initially as a limp. Even if this is not the case here, it would give the bird a bit of a pick-me-up anyway. I'll paste it at the bottom.
So, check her over thoroughly, worm her, boost her diet and then see if the limp passes over the next few days.
A sick bird can often be helped by the Rickets diet. Feed the birds once a day for three days or until you feel the bird is looking and acting better - usually 3 weeks.
This amount feeds one bird. Each serving consists of:
½ to 1 x cooked egg yolk… crumbled into mixture
1 teaspoon of cod liver oil..
1 very small drizzle of honey
2 x tablespoons natural yoghurt - no sugar
2 to 4 tablespoons rolled oats or Baby rice
1 dessertspoon of beef tin cat food…… Not dog food
A few grains of multi vitamin powder
2 tablespoons of grated apple..
Mix to make a crumble mixture not runny, if you have to roll into pellets and force feed, and then gently massage the neck in a downward motion to get it down into the crop, then do it, the bird may be too weak to eat or have lost the desire to eat….
Always have fresh clean water available at all time for the bird and good quality food
Feed the rickets diet in the morning. Also have her ordinary feed and fresh clean water available at all times: if it has not been fully eaten with in 12 hours throw it out... make another one the next morning.. don't add to it.. clean out the dish it was in also before adding the new mixture.