ETA: And when I counted the eggs on Friday she only had 9/10 under her. I'm thinking she ate one? I double checked my cartons to make sure I didn't pick it up by mistake.
I have had eggs go missing from under Broodies before. I think they know more than we give them credit for and they eat/abandon those eggs that aren't developing.
I once kept replacing an egg the broody shoved aside under her. (A great big green one, so I knew it was the same one each time) That hen hatched every egg under her EXCEPT that great big green one. Seems she knew. I never candle eggs under a broody....irrates the hen and gives me a headache....but I also never take orders for chicks until they hatch....cuz you know "never count your chickens before they hatch" LOL