Help! Can female Canaries be Sterile?

[nicoletta]

I have a female Gloster Canary named Mrs Potts from Beauty and the beast. She looks like a fat round tea pot. I just love her. Anyway, I was so excited to see her building a nest last month. I thought she was going to lay eggs like the other two females in the cage, but she still has not laid eggs. We have have two males and 3 females. The other two females both laid eggs that should hatch any time now, but Mrs. Potts still has no eggs. She built this nest and she goes in the nest and sits like she has her own eggs. She stays in the nest all night and for many hours of the day just like the other two canaries, but still nothing. She is not egg bound. She poops just fine. I have only seen the male mount her one time. Has anyone seen this behavior before?