eldest daughter; first-born daughter
Refers to the oldest daughter in a family. In families with only one daughter, she may also be called 長女 even though she is the only daughter.
彼女は三人姉妹の長女です。
She is the eldest of three sisters.
長女は来年大学に入学します。
My eldest daughter will enter university next year.
She is the eldest daughter of three sisters.
As the eldest daughter, she has to support the family.