Mysterious Disappearing Dummy Egg??

I have my local breeder coming to clip my birds wings for training (I know how some of you feel, this is a last resort option for me!) and my hen should be done nesting with the dummy eggs. I have calculated that she should've been done last week and left it an extra week for her to realize they are "duds". I checked the box on a whim last night and found 4 dummy eggs instead of the 5 she "laid"??? I am unable to locate the missing one (I tried a few times quick, but to no success, she was attacking me heavily each time)

Here's the problem - She looks ready to lay a replacement egg?? She has all the signs - very round back end and her vent is visible again. She looks the same as when she was laying before. I am sooo ridiculously frustrated at this point. I still want to move ahead and switch cages, remove the box and clip them. Will this stop the laying, especially if she already has an egg on board?

The previous owner did not mention anything to me of them nesting (she let them free fly 6 hrs a day) and this starting within 3 weeks of me having them. Am I doing something wrong, or something very right for them to feel safe to nest? (I cover them early each night and took out the snuggle hut as soon as I realized my mistake. The nestbox was for this nesting period only with the dummy eggs)

FOUND THE EGG! Was buried in a corner of the nest- had to completely kick them out and remove the cage from the room to find it! LOL! So, now what? Will she still drop that extra egg?