Is she back in the brooder? She sounds cold, but could be sicker than that. If she was stepped on, she will get better, or not. You can't do much more than get her warm (75 is too cold IMO for 4 weeks) - put her under the heat lamp/brooder lamp. Try to get her to eat- wet some chick mash, consider giving a few drops of electrolyte water. You did not say what she normally eats- if they are not on medicated start, and you have recently put them outside on dirt- you may have a sick chick from coccidia. Put in paper towels in the brooder so you can see what the feces look like. Meds for the water are available if you think they have coccidia- typically presents as ruffled lethargic chicks (or even sudden death) with diarrhea- recently put on dirt, and not on medicated start.
