The picture is not clear enough to really tell. Is it still there? Could be a soft shelled or malformed egg shell, in which case you can pull gently and see if it will come out. You can soak her in some warm epsom salts and use some vaseline or ky jelly also to help loosen it. If it's not egg shell material then a better picture would help.
Hopefully it was just a one time glitch. As long as she's acting normally then I would just keep an eye on her. How old is she? Sometimes new layers will have glitches, or they can have glitches when going into, or coming out of, molt. Do you have oyster shell available all the time for calcium? Not enough calcium can contribute to soft shelled eggs.