I would give it orally just like your doing. I have heard the Tylan50 is bitter, so maybe a nice treat afterwards? A couple of mealworms, a few berries, etc.:)
With injection you risk injection site necrosis - even if that did not happen, I would think after 5days being stuck 2X a day, even...
If you can give it orally 3 times a day, then use .20ml per pound of weight for 5 days in a row. That will give you the "mid-range" dosage.
If you can only give it orally 2 times a day, then give .30ml per pound of weight for 5 days in a row.
Only treat the birds that are symptomatic...
Tylan50 dosage according to Plumb's Veterinary Drug Manual is 10-40mg/kg given twice or three times daily. Tylan50 dosage has a wide range. If your hen has a severe infection, then go with a higher dosage.
What do you think she has? Mycoplasma or other respiratory illness?