Why would she suddenly start laying soft shelled eggs?

Foods high in protein are good when a chicken is going through a molt. They need alot of protein to grow new feathers.
Meats, fish, worms and cooked beans, especially soybeans.
NOTE: The trypsin in all beans is toxic to the lining of the birds' intestines. It can scar their intestines, making them less able to absorb their food. Any beans fed to chickens need to be at 180 degrees for 15 minutes to destroy the trypsin.
Good link to protein for chickens:
http://www.lionsgrip.com/protein.html

Celtic Druid: I am starting to break the cycle of egg eating. What I have been doing is in each nesitng box I place a rock that looks like an egg, or you can buy wooden eggs. They peck at them and it discourages the behavior. The second thing that I have been doing, is going to the store and finding some cheap eggs to buy (Only because I dont want to waste my tastey eggs) and blowing out the insides, Then filling them with mustard and anything else that you think they might not like. To blow the egg you can use a pin head and poke a whole in each end. Then straighten out a paper clip and stick it in the egg to break the yolk. You can blow the egg out with a straw or whatever. Then before filling it with mustard, light a candle and use the melted wax to plug up the one end. This next part is very messy, becuase it is difficult to fill the egg with such a tiny hole (which you can make larger, but its harder to plug the end up). What I have found to work out best so far is a syringe. Then once it is about 1/2 to 3/4 full you can plug the other end up with melted wax. They hate the taste of mustard, and when they get a taste of it, they start to stop. I will place two of the mustard filled eggs in the nests a day until there is not as much breaking. I hope you have success with your egg eating girls! It is soo very aggravating.

I had at least one hen who was laying very thin fragile eggs. I started trying to up the calcium by adding different foods because she obviously was not eating the oyster shell. Every day I mix a batch of partially cooked oatmeal, plain yogurt, BOSS, canned tuna, their own crushed egg shells and any kitchen scraps we have collected and feed them this yummy slop. They go crazy for it. I also have been giving them raw spinach leaves, cabbage and broccoli.

Powdered milk is a good idea, I am gonna start adding that to my slop mix too! My husband and kids think I am crazy... mixing up a big bowl of yuk. I even add meal worms sometimes. but my girls LOVE it.

And now...no more soft eggs!

Thank you, ksmith! I appreciate the info. It is aggravating, as is the soft shells.
Christie Rhae, thanks for the tip. I make my girls a bowl of slop every day too with oatmeal, kitchen scraps & whatever else I have on hand. They just gobble it up, crazy birds.
Link to another thread of the same topic if you want to check out the responses:
https://www.backyardchickens.com/forum/viewtopic.php?pid=6427703#p6427703