You really need to jump hard on this, because the other hens will soon learn from the egg eater and it's practically impossible to overcome this behaviour once it starts. People have tried filling eggs with mustard , so the offending hen gets a nasty mouthful, but you can't go on doing this for ever, and anyway, she may still be able to find and eat the good eggs the other hens are laying.
Probably the most effective strategy is to instal rollaway bases in the nestboxes. You can get plastic inserts which are set on a slope with a space underneath, so the egg rolls away out of reach of the hen once it has emerged. This is similar to what is used in commercial egg farms, and it also keeps the eggs clean. The only problem may be if your nestboxes aren't big enough to contain the rollaways.
Until you've solved the problem, one way or another, it might be necessary to isolate the egg eating hen so the others don't learn her trick. If you could separate her during the day, by fixing mesh across the run so she could still see the others, and provide her with a box to lay her own egg in, she could return to the flock overnight after they'd laid for the day.
In extreme cases, the only sure remedy may be to cull the egg eater, I'm afraid, as this bad habit is easily taught to the whole flock and then you're in real trouble.