Stop the grower, switch to raiser, and provide a source calcium for the hen?
My 13 week olds have their own coop and grower food. The older chickens have their own coop and layer food. They have a common run and go in and out of each of the coops.
I have seen the older hens eating the grower food from time to time, but they still lay as before. I haven't seen the young ones eating the layer food, but I don't monitor their world that closely.
None of the food is medicated.
I have one hen who is broody to make this all more complicated.
The chickens seem happy and healthy.
I decided not to worry about this.
Chris