When do females stop producing eggs?

I have a female homer who is five years old and in good health. She hasn't produced any eggs in about two months. Is this normal? I know that she is not egg bound, as she has been twice before and I know the symptoms. I give her a lot of vit D (since they are inside pets), calcium, and a variety of other vitamins and minerals. She and her mate continue to make the nest and sit in it, but she doesn't produce. I felt bad for her yesterday, so I put a wooden egg under her and now she just sits on it- as if she laid it.

Any advice would be appreciated.
Brooke