Yes they are 99.9% sure she's incubating. They have no access to the suspected nest area and there is no cam there so no one has seen to confirm the eggs or how many. The watchers have deduced by behaviour, she's on the ledge out of view and they have seen shift changes between Archer and Beauty and they've seen him bringing her food. During shift change she will sit on some fire escape stairs for a bit and preen and eat then she goes right back to the suspected nest site and Archer gets up and they switch places.