Waiting to see what happens.

Last week one of my hens was not acting herself. I took her to a vet who could not find anything wrong. We put her and the other hen on worming medacine to be sure. The poop sample brought into the vet did not show anything under the microscope. They are two 21 month old ladies. The hen was feeling better the next day....fluke maybe?
The week before that happened, I woke them in the morning to find that one of them had laid an egg with no shell while on the roost overnight. I would have never noticed it if the hens did not try eating it while I was right there. I brushed it off as an oops egg.
They have just finished their medacine. The egg laying machine ( Shirley the cinnamon queen ) has not laid since I took her to the vet that day, while Roxy the Plymouth barred Rock has stepped up to laying one egg a day. Before, it was one every other day.
While cleaning the coop a couple of days ago, I noticed that, yet again, there were a couple of frozen eggs with no shells in the bedding. They probably could not eat those since they were frozen. I also noticed that there were egg yolks splashed up on the walls.
Still, Shirley has not laid....except maybe those eggs with no shells?
She was the egg laying maching until she was not feeling well that day. She was laying one egg a day before all this happened. The shells were very good and hard from both girls.
They have layers feed and free choice oyster shell. I also mix the oyster shell in their feed.
I give them treats that are good for egg laying such as broccoli and cheese and meat to help them stay warm at night since I don't use any heat and the temps have been up and down like a yo yo here. Was 0 degrees yesterday morning and 30 degrees this morning.
So, anyway, I am wondering what is going on. I have all the patience in the world and will wait to see what comes of this. My girls are my sweeties and give me hours of fun and happiness and I want to take the best care of them that I possibly can.
Any thoughts on this?
Thanks so much. This is a fantastic site and you all are so very helpful.

 

Yes,
I forgot to add that the girls are getting extra light each day. I turn the lights on at 3 am and let them go to bed naturally as the sun sets at around 4:30 pm. It seems to have been enough as both were getting into the laying routine with one egg a day from Shirley and one egg every other day from Roxy. Roxy has finally kicked up to one egg a day now. But now Shirley seems to be laying shell less eggs? It is a deduction as I have only witnessed a few of them. I don't know if she is doing it every day.