Why is my hen not laying?

I have a pair of gold laced orpingtons. When I got them, they went to the quarantine coop. I wormed them with valbazen. She didn't lay for about the first week, which was normal since she was relocated. Then she layed two eggs that I threw out since they had been given the valbazen. When I moved her up with the rest of the chickens she stopped laying again, but its been over a month now. She has plenty of water and food. She gets the same as everyone else and no problems with the others laying. Does anyone have any ideas as to why she stopped or what I can do to help out?

She eats layer feed and she isn't molting. She has a nest box. I put fake eggs in it, but no luck. No signs of illness.

I got the pair at an auction, so I am not sure on age. I guess its possible I got her last two eggs, but I hope not. I was hoping to hatch her eggs.