You may have to cull her before she teaches the rest of the flock that egg = yummy.
Try putting a curtain on the front of the nesting box. The goal is to make it dark so she can't see it.
Some people will suggest putting hot pepper sauce in an empty egg. Chickens don't have the taste receptors for hot spices, so this won't deter them. You can try putting some blown out eggs in the nesting box so that if she breaks them, she'll learn (we hope) that egg = nothing.
if you KNOW what hen did it,, you need to STOP her NOW before she shows others how to do it... or you will have the whole flock doing it
#1 pick up the eggs at least 2Xs a day (more if possible)
#2 put fake eggs in the nesting boxes (wood, ceramic or plastic)
#3 some people put curtians up (i never have)
#4 make sure their DIET is correct.. could be nutritional..
#5 give them lots of other things to peck at.. could be bordom..
#6 cut just the TIP off of the top part of the beak,, might bleed a tiny bit.. if you dont use heat to stop the bleeding the beak WILL grown back.. but it stops mine from using their sharp beaks to break the eggs.. i do this, it is better than culling them.. at first at least, gives them a second chance...
if you cant stop her you need to CULL her.. NOW...
This hen is a polish hen that was given to me almost a month ago, and before today I didn't know why my egg production went down.
I collect eggs 2x a day sometimes I am out there more often, I may just cull
You may want to try to start your girls in a community nest box. Think of it like a corner base cabinet with no shelves in it and a flip open top. It allows many birds to nest together and because its dark and they can't see the eggs, it eliminates eating. Chickens enjoy the peace and quiet of laying eggs where its dark and quiet. Many will use one nest and none seem to get stepped on. Here is a pic of a nesting box . It can sit on the floor too. It also eliminates having more that one hen in a nesting box. This is better than having to cull a good layer.