How old is the oldest egg? I have heard of people putting 10 day old eggs to set or incubate, but I usually feel safer with one week old eggs that I have turned everyday. Also if she only just started laying eggs, they might be unfurtile. In my experience a pullet will lay, but a hen will set. Age of the girl is what I mean. We want maturity here.
If I want a hen to become broody, I make sure my nesting boxes has a few wooden eggs to fool her. Not only will the hens lay near other eggs by choice, but the broody types will start setting on them.
There will be no mistaking a broody hen. A hen laying an egg, will allow you to move her to check for eggs, but a broody hen will fluff up her feathers and make strange threatning noises to fuss at you for interfering with her work. She might even peck you if you aren't fast enough in the way you restrain her....you might grab her fast enough and still get pecked with a hen that has a long neck.
Bring in your eggs and start keeping track of which egg is oldest. You can date each egg with a permanant marker. Keep the eggs at a cool place, but not the refrigerator and turn them everyday a few times. It is easier to just keep them in a carton and turn the carton. After your eggs are over a week, and no sign of broodiness, just put in the refrigerator and eat, and continue picking up and marking them.
May as well tell you that once a hen starts setting, all the others will notice and they will want her to set their eggs. Her nest will quickly become the most popular and you will have to go every afternoon and pick up a possibly upset hen and remove the unmarked eggs, unless you can close her into a brooder alone. This will be a necessity. If you don't, you will have some chicks hatch at 21 days....give or take depending on the chick size and some die in the shell when she gives up on them and leaves with the first hatched. She might even be hard headed and stay until everything is hatched, which is a death sentence for the first hatched.
What you probably need to do is start off with getting to know you chickens well. Bring in the eggs. Go to the library and borrow everything you can about poultry raising. Its second nature once you get into it for a while.
Good luck.