OR...
Fill her up with yogurt and cod liver oil.
It might make her droppings a but runny but it is a fast source of calcium and phosphorous. the cold liver oil (Just a few drops) will give her Vits A & D3.
It's not an instant fix but will do a lot the help her out of the crisis.
For the future add some Battles Poultry drink to the drinking water each day - it contains lots of things including Phosphorus. Get some limestone flour (from horse feed shop). Give her about half a teaspoonful each day in some moist food that she will eat, I use moist layers mash but whatever you want to use e.g. mashed potato, porridge. would be fine.
Keep supplementing until egg shells are back to normal.
PS. My hens are laying rock hard shells and we have had more very hot weather here than any other part of the country.
