Candling is when you look at the egg using a really bright light to see what is inside (you can make/buy a candler or just use a really bright flash light)... you should be able to tell if the egg is good / there is a chick developing, usually by day seven or so it is pretty obvious... it is harder if the eggs are really dark colored like Marans eggs. X3 on check out the Hatching Eggs 101 article, there are some good articles in the Learning Center on eggs in general ... that one covers about everything https://www.backyardchickens.com/a/hatching-eggs-101
Two of the articles on making candlers and with pictures of the eggs at different stages of development, ie making a candler with a light bulb https://www.backyardchickens.com/a/...-egg-candler-using-common-household-materials and using a flashlight https://www.backyardchickens.com/a/pictures-and-videos-of-candling-chicken-eggs and lots of good pictures especially of the early days https://www.backyardchickens.com/a/candling-pics-progression-through-incubation-of-chicken-eggs
Two of the articles on making candlers and with pictures of the eggs at different stages of development, ie making a candler with a light bulb https://www.backyardchickens.com/a/...-egg-candler-using-common-household-materials and using a flashlight https://www.backyardchickens.com/a/pictures-and-videos-of-candling-chicken-eggs and lots of good pictures especially of the early days https://www.backyardchickens.com/a/candling-pics-progression-through-incubation-of-chicken-eggs
Sometimes it does take the broodys awhile to figure out what they are doing, they may stop and start and rearrange the nest until they are happy. Hopefully your girl will settle down alright and will have a good hatch!
