Is naming a daughter after her deceased paternal grandmother considered an act of filial piety if the father's intention is to honor his mother?

If the grandmother made such a recommendation, or if her desire for it was known, and there is no Shari'ah-related prohibition in the name, then doing so is an act of righteousness towards her and an honor to her. Just as naming children after individuals is an honor to them and a remembrance that prompts seeking forgiveness for them, it is among the commendable matters as long as it does not involve a Shari'ah-related prohibition or is not a bad name. The daughter has the right to be given good names.