Why won't this bird grow???

[KSH1]

I have 9 OEGB's, of course only 2 are pullets. And, of course, it's one of the pullets who refused to grow. Her energy is good, she happily zips around and ducks under bigger birds to get prime feeding spots, etc. She doesn't feel super skinny but the skin over her keel bone is bald. She still uses the heat plate, and her head still seems more like fuzz than feathers. They all hatched 4/22, so they're almost 10 weeks old. They're currently in the low-dose (.5tsp/gal) tail end of a course of Corid, but I did give her a couple of drops of NutriDrench tonight. I did a week of probiotics, but the directions say not to give it every day long-term. Is that "in general" advice; when trying to help a runt should I keep using it? I don't want to be missing something I could be doing or should be seeing. I know I could cull her, but I'm not planning to breed, and I'd like her to grow up and lay eggs! I appreciate your thoughts. All of the birds in the foreground of these pictures are OEGB from the same hatch.

Oh, and is her top beak too long?

 

[KSH1]

P.S. they started on New Country Organics starter, but I didn't like how they sorted out just the preferred bits, so now they're on Nature's Best starter/grower crumbles. I finally found a local source of Kalmbach, so I'm going to transition to the Kalmbach organic broiler crumbles, which are 22% protein (versus the Nature's Best at 18%).