The correct answer to this open question is the following.
If God Zeus comes to me and said that Olympus is lacking a god or goddess, and he needs me to help him, the new Olympian that I would invent would be Gioia, which means "happiness" in Italian. This would be its description
Name: Happiness.
Roman Name: Gioia
Connection to Olympus (related to another god or goddess? Niece of Zeus.
Married to a god or goddess: No, she would be single.
Powers: She has the power of turning sadness into happiness. The only requirement is that humans are pure of heart and consciously desire to be happy.
Symbol: Salamandra.
Personality traits: SHe is sweet and tender. Full of compassion, always smiling.
Friends: Diana, Minerva.
Enemies: Mercury, Vulcano.