It is! You have a special case. Where did you get her from? Hatchery leghorns don't because it has been bred out of them. Breeder leghorns may be different. Sounds like you have it under control! Let her at least see her flock, otherwise they may forget her. I had that happen. The hen was bullied and had to go through the integration proccess. At day 18, 19, or 20, I would block her off completely. That way any chicks that hatch will only be messesed with by mom. Made that mistake with my first broody too. Chick got out from under Mom, as they do, and got pecked in the head. Mom did not protect it. Probably because she was young, about the same age as your pullet. So like Perris said, she may not be a great mom. And you should candle the eggs on day 5 or 7 and check for viability. Then take the non viable eggs out. A lot of people candle again on day 10 - 14. When I had a broody, I think I candled day 3, 5, 7, 10, 14, and 18. I know I candle that often with incubator eggs. I have a bad case of OCD. (Obsessive Candling Disorder)