I was thinking about her being egg bound as well as a possible cause. I hope it’s not Mareks Disease eitherIs the lameness in one leg or both? This sounds gross, but if you or your parent could insert a clean or gloved finger inside her vent 1-2 inches, to feel for a stuck egg, that would be helpful. Since she laid a soft egg recently, I would give her a 1/2 calcium tablet or Tums orally now. Has she been eating and drinking today? She needs to be separated in a dog crate or pen with food and water right now so the others will not hurt her. Hopefully, she is eggbound, but hopefully, it is not Mareks disease.