This is what I would do. Mark the ones she has now with an X. Everyday she lays number the new ones 1,2,3 and so on and remove one of the older ones marked with an X with each new one she has. I can't imagine she will be able to set on more than 15 successfully so this way you give her the best chance by leaving the freshest eggs in the nest.
In the future when she lays again start right away with the eggs and numbering.
Also I would probably candle the eggs she has now and toss out(or hard boil and feed back to your ducks/chickens/dogs)3 or 4 of the oldest ones(these should be the ones with the largest air cells)