The Spanish feminine noun for the girl celebrating her fifteenth birthday is quinceañera.
The term can refer both to the honoree and, by extension, to the celebration itself in English-language usage. In Spanish, quinceañera is formed from quince, “fifteen,” with a suffix associated with age or years. The masculine counterpart, quinceañero, is used for a boy in related celebrations, though regional usage differs.
English speakers often use quinceañera as a general name for the party, while Spanish speakers may also say fiesta de quince años or quince años. These expressions emphasize the birthday or the fifteen-year milestone rather than only the person.
The title should not be confused with madrina, meaning a female sponsor or godmother, or dama, meaning a female member of the court. Those people may have important roles, but they are not the honoree.