Yes my lavs are crazy broody. I have one in a nest right now that wants to sit. Hope you find her! I recently lost an F1 pullet to a fox, a devastating loss for me since she laid a gorgeous blue egg, better color than the mother. Anyway, the pullet that was taken by the fox just disappeared like that one day. I did not find any feathers. It was not until later that I found a pile of feathers about 15\' outside my fenceline. I hope yours was not taken like that. Mine go broody in the nest boxes they are used to laying in. If yours was laying routinely in a nest box, it probably is unlikely that she would suddenly seek out a different spot to nest.
I put my labrador out with the birds now when I free range them. She is an excellent fox deterrent and does not bother the birds.