"Sa fille est une adolescente."
Translation:His daughter is a teenager.
Not sure if it is obvious, but how would you change this to her daughter is a teenager?
It would be the same sentence. Context will distinguish it for you.
But if the distinction is absolutely necessary, you may say "sa fille à elle est une adolescente."
It's the same sentence! When talking about possesion, the gender of the possesive term (sa/son) depends on that of what is owned. For example, son frère and sa sœur could both mean either his/her brother and his/her sister. The only exception is when the object begins with a vowel, which is when it will always be masucline (for the sake of pronunciation). So we'd always say son ami AND son amie, instead of sa amie or s'amie.