Muscovy duck incubating an empty nest

I have a wild backyard female Muscovy duck I call Girlie who built a nice feathered nest under a bush beneath my front window. For about a week she came to it a lot and set it up nicely and maintained it, and even sat there a while. I thought she was laying.

For the last week and a half she has been sitting on it full time with a break a day to eat . Males sometimes guard the area and mate with her. Sometimes several one after another. At times right on the nest where she is sitting!

When she leaves I have been checking the nest and there are no eggs. Once I found a round white rock, and once a snail shell both of which I removed.

So, what's going on here? Is it normal for a duck to sit on a nest constantly even when it is empty? Is she hoping to lay some eggs and practicing for that event? Has she just found a comfortable spot to rest?

Here is a photo of Girlie on her nest and one with a male guarding her while she sits (you can see her in the background).



And here is the empty nest with all its feathers. It would be a nice place for some eggs to hatch....

She probably will la soon. She it just preparing.

Girlie ended up abandoning her nest a few days ago. She never laid an egg after 3 weeks of sitting there. Too bad. I would have liked to see her babies!

That weird that she didn't lay.

I have a Muscovy duck sitting on her unfertilised eggs for approximately 3 weeks before I removed them because we have no male to fertilise them for her. She returned straight back to her empty nest & has been sitting there eggless for another 2 weeks.Trouble is she attacks my hand when I go near her & is threatening to my other smaller duck breeds in the pen. I am worried she will attack them if they get in her way. Can anyone advise me how to make her see sense....She is a rescue duck & now she has turned her frustrations on to anything that moves really. Its obvious that she still thinks that she has her eggs & that they are fertile & contain a new clutch. Help! Not sure of her age.....but have had her for about 2to 3yrs now.
Please advise if you have any answers that are viable....Thanks in anticipation.