The way I understand you, this second hen has fully recovered and is no longer sick. In that case, what is the issue?
Your original hen is dead and buried, so that case can't really be explored further. A necropsy, even a cursory amateur attempt, could have been enlightening as very often what killed the chicken is staring you in the face when you open up the abdominal cavity.
If you have another chicken get sick and die, it would be a good idea to be thinking about where and how to obtain a necropsy.
If you wouldn't keep your location secret, we could help you find this information.