Can you post a recent picture of her? Is it possible that she is hiding her nest? I don't think this is common in in Leghorns, but I know other breeds can go around 1year old before they start to lay. Game breeds can go longer than 1year old before laying a egg. I think she could have her own reasons for not laying. Unless she is a he then she should start pretty soon, but on rare occasions a hen might not ever lay or more commonly (mostly hear of it in hatchery birds) be internal layers or have some kind of laying problem.