Letting my hen hatch her eggs

[therealestchicken]

Its day 12 that my hen has been sitting on her eggs, but when she gets up to get food or water i keep finding more eggs. I tried to move her to the fromt yard in a small coop but she freaked out and ran back to her spot in the backyard. she was sitting on 14 and now theres 18, I cant tell them apart. How can i stop this? should i lock her in the coop in the front yard?

 

[LaFleche]

Other hens are adding to the clutch and the eggs will all be at a different stage of development causing a staggered hatch.

Next time she leaves the nest, gently gather all of them in a padded basket or similar and bring them in for proper candling.
Best done in a dark room or closet using a strong flash light.

How many eggs did she start with for you to know that it is day 12?
At day 12 of incubation the eggs should look like this when candling:

https://www.backyardchickens.com/forum/uploads/230_day_12_1_copy.jpg

I would remove all other eggs from the clutch that do not look like the picture above or very similar, to ensure that the remainig eggs will hatch around the same time (usually 2-3 days).
Then mark the eggs and give them back to the broody.

Check every day for any new additions and remove them accordingly.