With all the nesting material pushed behind her and her tail spread she tries to make herself look bigger to put off the blue tit on the outside of the box looking in through the hole. This carries on for about 20 minutes before she eventually leaves.
For reference have a look at her cap. It’s got a pale pointed area at the front and looks like it almost joins to the dark ring around her neck on one side at the back. This is how we differentiate the birds that visit and how we know that this is the last we see of this hen.