That is correct - since your mother was not a resident of PA and the property you inherited was not located in PA at the time of her passing, it is not subject tp the PA inheritance tax.
From Pennsylvania Inheritance Tax & Safe Deposit Boxes:
"In the case of a nonresident decedent, all real and tangible personal property located in Pennsylvania at the decedent’s death is taxable. Intangible personal property of a nonresident decedent is not taxable."
