A lash egg is less of an egg than it is a roughly egg- or sausage-shaped exudate, consisting of thickened pus and other materials. It is probably the grossest egg your hen will ever lay, and will often look like cheesy, bloody strata or other matter arranged in strappy, skin-like layers. You may think she's expelled an internal organ.
If your hen lays a lash egg, it means she is sick with salpingitis, which is an infection of the oviduct. Please take her to a veterinarian immediately.