Delaware allows part-year residents to file either a resident or nonresident return. Per the Delaware Individual Income Tax Return Instructions, you can choose to file the one that is most advantageous for you. Filing a resident return is better if you had no income from other states during the time you weren't a resident.
Filing a nonresident return is more advantageous if, during the period of non-residency, you had any income from other states or sources outside of Delaware. You will still be able to claim a credit for taxes paid to Pennsylvania while you were a resident of Delaware.
In the question that asks for PA income, you should enter the amount of money you made in Pennsylvania while you lived in Delaware.
Delaware Individual Income Tax Return Nonresident and Instructions
