Hugh, yes I believe you need to try to get her to accept the wren guard; however, as you said it would have been better to install it after the 1st or 2nd egg was laid, prior to incubation. Since you put a hinged guard on the Gilwood box (which is exactly what we did at first – then made it a top opener as well as a front opener later) I would give her a little time. Catch her some time when she is taking a break from incubating & try putting it down. If she doesn’t accept it after she is back at the nest for 10-15 minutes, then put it back up. I have never had a female refuse the spooker or wren guard, but then I always have them up prior to incubation. Good luck – let us know how this plays out. REMINDER – there needs to be a minimum of 2 1/2″ (3″ is better) between the actual hole & the guard to allow for an easy swoop into the box. Do you have spooker & guard up at the other box which has 3 eggs? Just because you don’t see these predators doesn’t mean there are not around – it’s up to us landlords to protect the nest, since we invited the birds in.