She's cute. She is mallard shaped but her face looks like a Rouen to me. Or I haven't seen enough mallards yet. Maybe she doesn't really know what to do as a first time mom.
I used a small flashlight witd LEDs, the aircell is on the round side of the egg so that's where you put the flashlight...
That is a lot of eggs! I thought mallards would lay around 12 eggs and then sit on them. Do you have a picture of your female?
Not sure if you can spot a rotting egg with candling.. But you could candle them anyways :D