The eldest daughter in a family; the first-born daughter (may also be used if she is the only daughter).
彼女は家族の長女として妹の面倒を見ている。
She, as the eldest daughter of the family, looks after her younger sister.
長女は大学に進学した。
The eldest daughter went on to university.
長女（ちょうじょ）は時に家庭で重要な役割を担う。
The eldest daughter sometimes takes on important roles in the household.