11week pullet tail drooping, trouble walking

[ErvinFlock]

This looks like what happened many years ago to one of my young cockerels that gained too much weight for his still soft and weak bones.
He walked and sat like a penguin for about a week and seemed to be in pain, but then the treatment showed effect:
More vegetables, calcium + VitD3 + K, less carbohydrates and protein.

He recovered but I culled him two months later, as this is a genetic predisposition I don't want in my flocks.

He hatched from shipped eggs I bought from a reputable breeder.

Thank you for taking the time to reply. She was hatched from my largest bird who is heavier than my rooster. I could see how this may be the problem. I can control her feed and will do just you said.