only daughter
Refers to someone's sole daughter. It says there is only one daughter, but context determines whether there are also sons.
彼女は一人娘として大切に育てられた。
She was raised with great care as an only daughter.
The president's only daughter took over the company.
She grew up as an only daughter.
My father dotes excessively on his only daughter.
We decided to bring in a son-in-law for our only daughter to carry on the family.