It depends if she laid the eggs and if she did were the fertilized?
Candeling is when you check if there is any development of chicks inside the egg by holding the egg to a bright light making the contents of the egg glow........ I use a small LED flashlight ...... Then hold it up to the large end of the egg on an angle so there is no light escaping between the edge of the flashlight and the egg.
BTW by day 20 I wouldn't candle because if the eggs are firtle and didn't die during incubation they would turn out black inside of the egg because of the size of the chick.