I'm sad over this news. Yes, you have two choices to find out what was going on inside the hen. First thing to do is chill her body, do not freeze, in the refrigerator while you decide.
Next, you can locate an animal testing lab to get a necropsy or you can decide to open her abdominal cavity...
Did she aspirate the liquid? Did she choke when you poured it into her beak? Is she breathing with a troubling gurgling sound?
There is a way to give liquids without risking aspiration, but pills can be given to chickens without going to all the trouble of crushing them and putting them into a...