единственная, у кого есть

the only one who has

→ единственный
phrase Rare #43,564
the only one who has Used when addressing or referring to a female person; единственная agrees with the feminine person, while у кого есть means “who has.”
RU: Она единственная, у кого есть запасной ключ.
EN: She is the only one who has a spare key.