Yeah, I tend to agree with you @aart.
A peck could go thru the shell but not penetrate the membrane.
Maybe a shell gland malfunction?
I have had a girl who used to lay eggs with shells that were just strong enough to hold the egg together, but not soft and rubbery. If you picked up the egg it would keep it's shape, but if you rubbed your thumb across it you would see the shell crumble underneath it. Anyway, THAT girl used to like to peck a little hole into each of those eggs - probably because (as with @mrross's egg) there was an easy access point. She never actually pecked into the membrane either, and we were still able to eat the eggs - although I was always careful to use them first.
I do wonder if this is some sort of shell gland issue. I doubt it is a lack of calcium, as the rest of the shell looks fine. Has this been happening for very long I wonder, or is it a 'new thing' she is doing? If it's only new it may just be a glitch in the system that could pass of it's own accord.
If it's been something that's been going on for a while, you could try a vitamin supplement with her, and also add some extra calcium to her diet (you can buy liquid and powdered calcium suitable for poultry that gets added to their feed) just to make sure she has adequate quantities of everything she needs.
I don't normally recommend extra calcium when hens are already on layers feed,
but that being said....I did once have a girl who (like the rest of the flock) was on layer's pellets and she consistently laid soft shelled eggs for a couple of months. Three weeks on a calcium supplement and she was as good as gold. I guess some birds just need that extra support.
Good luck!
- Krista