It's given in the water. You will have to do a bit of math, but the dosages are listed for different concentrations. You probably won't want to eat eggs she lays during treatment, and don't give them to kids, as tetracycline can stain adult teeth in children. You can startvout at 800 mg if you feel she is showing signs of infection. Taper down slowly and mix fresh every morning as it looses effectiveness over time and is useless after 24 hours. So you could start at 800 mg for 2 days, then 400 for 2 days, then 200 for a week. If there is any infection that should clear it. She may have diarrhea. She will need probiotics after treatment, like yogurt, to get her digestive system on track again. If there is a local vet who will see chickens and you are still concerned, I'd take her to the vet.