Cool project!
For naming Pennsylvania's divisions, could I suggest
Philadelphia for the Philadelphia area,
Susquehanna for the area that largely contains the Susquehanna River and encompasses the Lehigh/Wyoming/Susquehanna valleys,
Appalachia for the area that's covered by the Appalachian Plateau/Mountains, and
Allegheny for the Pittsburgh-area division?
Edit: I see from reading one of your replies that you already decided on Allegheny! I feel like if you wanted to retain the name of the original state "Pennsylvania", you could label the north/central PA division with that, as either "Pennsylvania" or "Appalachia" would be appropriate for that area. I just have a bias against names starting with P, since I think it's an ugly letter.