Occasional Soft shell

One of my girls used to occasionally lay eggs with a soft shell. I was given the following info/advice:

Make sure they have plenty of fresh water (in all weathers)

Plenty of grit mixed in with their food. We opted to bake and the ground down the chickens own shells and mix it in with their corn (which also had oyster shell mixed in it)

I was also told that if the bird is spooked/frightened in any way i.e loud or unexpected noises this can also cause soft shell eggs. Also if shes quite new to your home she may still be getting used to noises and surroundings, therefore may just need to settle in.