Hope she will be okay.
I had a similar thing happen with one of my Light Brahma's (9 weeks old), they were all in their run, and I came out to give snacks & Clara was not there. I did a head count, checked in the coop, they check the outside of the coop & run, nothing. No feathers, just nothing.
Went in & told Hubby, and 30 min later he went out to look. Backtrack a week, was growing grass in Rubbermaid dish pans for them, they ate all the grass & were digging in the dirt. Most of the dirt was gone in a few days from all the scratching & digging. Lena, the other Light Brahma was standing on top of the overturned container, hubby went over & lifted it up & out came Clara. I gave her a firm talking to that night about playing with containers, it was removed that day.
I also had a 5 gal. bucket that is use to hold their feed, too it in the coop, but forgot the lid. I put the bucket up on their roost (4 ft high shelf). Went in and got the lid, came back & did a head count, missing Baby Girl (my Barred Rock), I start looking again, and something made me look into the bucket. There was Baby Girl, happy as you please, sitting like she was trying to nest. A few days later, we got our first egg.
On the bright side, it was my RIR and she was a tad aggressive anyway. I also was 1 too many for my floor space, so this brings me back into agreement with the formula.
