Welcome to the forum!
Glad you are here!
I've had some that want to lay somewhere other than the nest box. If they are laying somewhere other than the coop and run, I just lock them all in the coop and run for two or three days. That's worked for me so far. But that's not your problem. Yours is laying in the coop, just not in the nest.
I made my nests so I could lock a hen in them if I want. I have had hens that have made themselves a regular nest on the floor and consistently lays there. When I catch her in that nest laying, I lock her in the nest box until she has laid the egg. It usually takes about a half hour and one time, but I had a Speckled Sussex that took over three hours and I had to put her in again the following day. That was a stubborn hen but she did get the message. If you are not there during the day this may not help much but maybe you can catch her laying on the weekend?
I am a firm believer in the benefit of a fake egg staying in the nest all the time. When a fake egg got scratched out of the nest, I had a hen lay next to that egg on the ground. She usually laid in the nest. When I put the fake egg back in the nest (and raised the lip on the nest box so it was harder to scratch out the fake egg), she went back to laying in the nest. If yours has established a nest on the ground, putting a fake egg in the nest may not change her habits, but it won't hurt.
I can't help on getting her to resume laying. She may be hiding a nest on you, but it doesn't sound like it if she normally lays on the floor in the coop. This time of year, many of them slow down or stop laying due to the days getting shorter. Some of mine are molting and have just quit laying. Some have not started molting but have really slowed down laying anyway.
Good luck! Hope this helps. And again,
