Siren Daughter (Olympian Exiles #1) by Cassie Day

A determined siren. A journey for immortality. A bargain shaking the realms apart. Seventeen-year-old Agathe is a siren, a creature once known for their enthralling songs. But her ancestors’ exile locks her and her family deep beneath the Akri Sea. She resigns herself to an unremarkable life with only her beloved mother for company. Yet when everything she holds dear is stripped away during a bitter winter, she embarks on a deadly quest. One for the most precious gift in all the realms: immortality. Bargain upon bargain, she travels across the realms to formidable god-king Zeus and his gilded palace. In the stark corridors and fracturing court, death and loss, friendship and love wait around each turn. But when betrayal renders a bargain with Zeus fruitless, Agathe must choose: her family or herself. One last shot at bargaining with Zeus. But every bargain has a price. If you like Greek mythology, slow-burn romance, and mythological creatures, you’ll love Siren Daughter, the first book in a spellbinding fantasy trilogy.