Kratos's daughter in the original God of War storyline is named Calliope.
Calliope is the child of Kratos and Lysandra. She is central to the emotional backstory of the Greek-era games, because Kratos's actions under Ares's influence lead to the deaths of both his wife and daughter. Their ashes later remain on Kratos's body as a lasting reminder of the tragedy.
The character's story is especially important in God of War: Ghost of Sparta, which explores Kratos's memories and family. Calliope also appears in the broader mythology of Kratos's past through visions and narrative sequences.
Atreus is Kratos's son in the Norse-era games, while Lysandra is Calliope's mother. Pandora is a separate mythological figure associated with God of War III, so none of those names identifies Kratos's daughter.