Thanks Guys. Yes she is older, nearly 4 years old. She, and her sisters are totally free range, until I have to chase them off the newly sown patches in the lawn (grrr!). The others lay hard eggs, albeit sometimes in not where they are meant to. We are in Germany, and as you may have seen we have had LOTS of rain (we're luckily not flooded here), so missed a lot of sunshine too. They do have a pot of grit and stones, but I will also try to feedback crushed eggshells, got to be worth it, and very recycling friendly too.
Thanks.