I STILL have an adult bird laying premature eggs on ground! WHY?

Hi folks. My cute little leghorn was the best layer of all our 6 birds. She's not quite a year old yet but for 3 months I swear she laid 99 eggs, never missing a single day, all healthy eggs. Always laid in the nest, even all winter. She has fulltime access to oyster shell and shredded fresh mozarella cheese everyday. 

PROBLEM: Now starting about 5 weeks ago, she just drops an egg out wherever she happens to be walking in the morning. She doesnt even look back, just keeps walking to catch up with the other birds. These eggs left on the ground are thin shelled. They crack just by being picked up. It seems like she laid them too early by just a few hours. Still she sadly hangs out in the nest area mid-morning, even sitting on the nest (she doesnt know she already laid!). I wish she would hold her eggs in and wait to lay them when the time is right. She is not new to this. I wonder if she is too excited to get out in the run every morning that she pops out an eggs from excitement. Is that possible? 

Any advice?

The cheese is a treat that I read about here. They only nibble on it occasionally.  The intention with cheese is to boost the calcium. Sometimes we give yogurt too. I also give catfood and tuna for protein. Of course they have layer feed too. 

I cannot think of what may have changed since this problem. I really think she is too excited. She is a hilarious busybody and always first to everything. She doesnt even notice she laid the eggs.