Anna, your post has brought back some memories of my birds. Both Bonnie and Edge used to lay eggs quite often. I well remember my surprise, and yes, even wonder, when Bonnie first did! Thats when I figured out she was a girl and changed her name from Bono! And again with Edge, but I didn`t bother changing her name. I always knew when Bonnie was planning to, she used to do this sort of mating ritual, can`t explain it but it involve a lot of tail in the air stuff prancing and a noise that would grow in intensity and she would be as if she was in a trance, I used to call her behaviour `egging`, it could get real annoying at times too! Edge was never as bad, though they both used to worry me when they were laying because, Bonnie especially, used to lay a lot of eggs over a short time. I used to get bird type supplements and make sure they had plenty of cuttlefish bone and mineral blocks. And they would fight, or rather whoever laid they eggs would go for the other if they came at all close. I tried to get them nesting stuff but they wouldn`t use it, yes, I know they weren`t fertile but they, Bonnie especially, used to get really upset if I took them out straight away, it was so pitiful, so I used to leave them a day or two, depending on when she would lay another, if any. After Edge died Bonnies laying gradually tapered off until she stopped altogether, though she still would start egging it sometimes, but not for too long.
As for why Rilla should start laying now I have no answer. I do know that Bonnie was doing the egging thing for a long time before I got Edge and before she layed any eggs, (it was only later I made the connection), she and Edge started around the same time.
I wonder if Popcornbird has ever had her birds lay eggs, bet we will find out!