Chickens become egg bound. Often times, when hens are egg bound, their vent will looks really gross. It will be distended, and possibly slimey (white and/or clear slime). The hen will become depressed, and she will stay as stationary as possilbe, waddling when walking. She may also become pale and lose weight. Feel her abdomen, you should be able to feel an egg if she is egg bound. Sometimes shelless eggs get stuck. Those are tricky to fix because you can't feel them and they can't usually be pushed out. Soak her in warm water for a while to relax the muscles, and give her one 200mg Motrin pill (it will reduce swelling). If that doesn't help and if you still feel that she is egg bound, take her to a vet and ask if they can give her a shot of Oxytocin (will cause contractions) and some kind of heavy duty antiinflamitory (medacam is good). Push against the abdomen to force the egg out. If you can see it in the vent, then let the hen do the rest (they'll usually get it out at that point). Breaking the egg is a last resort.
But, like basicliving said, she might still be broody. Good mama hens sit on imaginary eggs. Pains in the butt they are. lol.