Lumpy eggs

:/Have one out of twelve hens that is laying deformed eggs, she 18 months old and seems healthy. They have lots of lumps or bumps at both ends of the egg; also have tiny groups of bumps that can be rubbed out all over the egg(tiny ball shaped). This has been going on for about a month; some of her eggs seem to be thin or weak. I leave crushed oyster shells in a small rabbit feeder for the flock to consume as needed and feed them layer food, good table scraps and free range around three hours a day. Have good pics of these eggs, but cannot attach them because I'm a New Egg! Any help would be great, thanks Dewey