It is possible and very unfortunate if so that your bird might have a tumor that is affecting its leg. My parakeet had a tumor that pressed on his leg causing him to limp. This is the worst-case scenario but tumors are common in parakeets, especially if they were inbred. Any type of limping however is serious in small birds and my advice would be to bring her in to a vet that specializes in birds.
I used old stretchy fabric and made "hammock" that spread across the cage so that my bird wouldn't strain its other leg from using it so much. However I think that if your parakeet is still using the perch rather than sitting on the bottom of the cage, she might not need that.
It sounds like the other parakeet injured itself. Since I am not an expert, I think the best thing to do is to bring both of them to the vet, especially if the limping gets worse.
I used old stretchy fabric and made "hammock" that spread across the cage so that my bird wouldn't strain its other leg from using it so much. However I think that if your parakeet is still using the perch rather than sitting on the bottom of the cage, she might not need that.
It sounds like the other parakeet injured itself. Since I am not an expert, I think the best thing to do is to bring both of them to the vet, especially if the limping gets worse.