'Lemon'.... as in 'Lemon Law'..... is slang for a defective product, usually an automotive vehicle.
It is applied to many products and/or situations that produce below standard or less than expected results...like an of age female chicken that doesn't lay eggs.
It was suggested a couple times earlier in the thread that you cut out all other foods except the layer feed.
Layer feed is usually the bare minimum in protein(16%) needed for egg production, any other foods given dilute that protein.
That combination can reduce nutrients enough to not support the bird making any eggs.