I'm with dawn on this. The diet that she's getting is very very much not what she needs.
Grains are high in phosphorus. Phosphorus is necessary for calcium absorbtion, but a full-grain diet will suck the calcium out of your birds - even out of their bones.
Unless you're highly experienced in designing a complete balanced ration for chickens, layers must be on a laying ration. It's cal/phos balanced and contains enough protein and other related ingredients to not only clothe the bird (feathers are their first line of defense) but allow the egg laying not to deplete their body.
Boiled egg and cheese won't do it long term. Yes, please buy some laying food and use the grains as 10% or less of their diet to keep the calcium balance good.
By the way, just providing them calcium supplements won't come near to providing enough for a bird to stay healthy and lay.
Please also don't worm her until you figure out what's wrong! She's too weak. You need to build her up first. I'd recommend ddawn's supplement to the laying pellets you're going to buy.
Make sure she eats. She might not like the pellets at first. try putting them in the blender if she doesn't.
Incidentally, also check her carefully for mites, etc, still. Did she have any? Did you see any when you bathed her?
Sounds to me like she's anemic from a possible infestation and an incorrect diet during which she layed admirably. It's ok that you were feeding her that way before - you apparently didn't know. So many people recommend grains because they're "natural". that's all well and good - if you are trained to design a complete feed. But scratch grains are only a treat. Complete rations are the way to go.
Honestly, I had a course in feed design, two courses in poultry nutrition, another course in aviculture and the total design of the avian body and its metabolism - and I even I feed complete feed.
I hope your bird does well. Please follow ddawn's feeding advice, and please let us know how she is. I'm sorry if I sounded a bit frantic - it's just that time's of the essence, as you well apparently know.