Teen daughter is travelling alone for first time. She is flying United out of BWI to EWR. She will then connect to international flight to Dublin. On the BWI side will she check in to International or Domestic flight?? Also, at EWR will she need to retrieve bag and then re-check it for flight on AerLingus? On return trip she flies AerLingus to Boston; then connecting JetBlue to BWI. Will she have to retrieve bag and recheck in Boston?