Thin dewormed pullet won't gain weight, tips for improving digestion?

Dear all,

Just wondering what has helped to improve the digestion, if a bird is constantly thin but eating well?

I have a 9 months old little hen, never laid an egg yet, for the last 2 months or so she's been perpetually thin. The poop sample came back as having some cocci which we treated with Baycox and, as I noticed in other cases sometimes, some days after there were some worms in her poop (which did not come up in the analysis apparently).

So treated her with Ivermectin and 10 days later with Levomisol (sp?).

Still the same picture, very thin no matter what she eats. Her appetite is ok, she gets a small cooked egg daily with some plain bio-yogurt (with the good bacteria) + Weetabix crushed in it as per our vet's suggestion. She has Growers in her dish all the time but not too fond of it. Also as the doctor suggested, I am giving her more natural food, to the point of recently taking her outside on our doggy walks now and lifting rocks for her so she can catch worms.

Her poop is of two kinds: either very foamy yellowish stuff (in which I used to find the worms), or very watery, clear poop (hard to even call it poop) with some bits in it which look like soaked pellets. Only after a night i find poop under her which looks like decent poop, more or less hard with white on top.

Oh, and she tends to drink quite a lot during the day, and sometimes, I believe, she has a bit of an impacted crop which won't go down, so then I give her some oil and yogurt and she's fine in a few hours.

Question.... what DO chickens need to help them digest better? Grit maybe? More greens (grass, vegetables - she gets some every day) What makes their system work better and more efficiently?

Thanks so much in advance, I really want to help my little girl if possible.

Wow, thanks so much, I will contact our vet regarding this! I've heard of this drug, just not under the brand name you mentioned, but we can get something like that here I'm sure! Thank you so much. Will give it a try for sure.

I just now noticed this...

For the Flagyl, my girl weighs 450 grams (that's like 1 pound, right?) and the doc prescribed 0.4 ml of Flagyl morning and evening.

Levomisol we added to their water, I don't remember but I think it said on the bottle how much it was per litre of water...