Originally Posted by
fairviewroad
Most Keystone departures from Lancaster do not stop at EWR. Getting to EWR generally requires a connecting train in Philadelphia. Alternatively, you could skip the connection and just ride the Keystone to Newark's downtown train station, then cab it to the airport. It's a short and relatively inexpensive cab ride, and it eliminates having to figure out the Airtrain system.
I wasn't even thinking about that, but your right. You would have to switch trains. Well for the OP's purpose they would probably be best off taking your idea and taking a cab from the Newark train station. For a reference for others there is also a city bus that runs the route.