Thank you all BYC Family! *smile* I feel very supported here. Sorry to reply so late, my phone typically let's me know I have replies, but didn't for the past three!
Little Carrie Bradshaw (yes, the other three are Samantha, Miranda & Charlotte)

seems to be better. I massage her each night and right afterwards she poos. She doesn't seem to drink enough water though. I'm considering using the eyedropper, but she's soooo squirrley, it's hard to get her to chill out and accept any kind of 'assistance'.
Thank you for letting me know that Leghorns are slight, and yes--she totally resembles a bird bird and looks less like a chicken, especially since the other three are filing out so nicely.
I've watched her free range habits and she goes straight to the longest, toughest grass/plants in the yard and I guess my BF caught her trying to eat a hair tie yesterday! (previous home owners left bits of rubbish all over yard, so it's not too hard for us to imagine her finding all sorts of indigestible items *bleh*)
She only jerks on occasion--it's happened the three or four times I've mentioned and has been aleiveated by massage. She appears healthy on all accounts, save her crop feeling like a hackey sac-- not all solid, but not all liquid- midday and niggt. At it's largest, it's about the size of a hackey sac too, but she's only about four inches tall and five inches long-beak to tail.
They share their nightly roost, sice their coop is not finished and I've been waiting for their feathers to come in. So I have been giving all of them yogurt mixed with chick starter. Is it ok to put them all on a diet to help with potential bacteria if they don't exhibit symptoms?
All in all, it seems like she's healthy. She's bright eyed, alert and probably my most active. As long as she's not supposed to be as big as the others. They'll be 8 weeks old tomorrow. She's still got downy feathers on her little head, but just today I can finally feel the adult feathers growing on her back. I would just feel terrible if there was something wrong and I didn't treat it right away.
My BF still thinks we should give her water via the dropper, but after reading so many warnings about getting fluid in their lungs/esoupagus I'm nervous. I probably sound so paranoid, but I'm a visual learner, so just reading how to do something to a creature w/ a spirit rather than a car or something, is not sufice. If anyone knows of a video on how to "flush a crop" (for future reference) or "give them mineral oil" that would be awesome.
Thank you all again!