If you had a broody, she would be setting on the eggs. You would know she is broody. Leghorns are not known for going broody a lot, so I would not leave them and expect one to take on the challenge.
One or more have decided this is a good place to lay eggs. There is no telling how old they are since it could be one or several laying here. If you want, you can do the float test. As an egg gets older, it loses moisture through the porous shell and the air sac gets bigger. After a while the air sac gets so big that the egg floats. If the egg sinks in water, it is probably still good to use. (No absolute 100% guarantee but I'd use it. Just break it in a separate bowl before you mix it in with other stuff.) If it floats, it may still be good but is a better candidate to cook and feed to the dogs or chickens.
You have a few options with the hen(s) laying there. You can simply collect the eggs from there every day, just like your normal nest boxes. You can block the dog house off where they cannot use it and they will find another place to lay. There is a good chance it will not be in the nest boxes, but you might get really lucky. You can lock them all in the coop for a few days. She might change her laying habits, start and continue to lay in the nest boxes you want her to. But then she might not once she has the option. I have had hens that were laying regularly on the coop floor. When I caught them there trying to lay an egg, I moved them to a nest and locked them in for about a half hour, until they had finished laying the egg. They learned after one or two times that the nest box was a better place to lay. That approach may not be feasible for you.
Good luck!!! Getting one to lay in the nesting boxes when she has other ideas can be challenging.
