Whose vs Who in this sentense?

Who's is a contraction of the interrogative pronoun, who, and the verb is
Who is = who's

Who's your best friend? = Who is your best friend?

Whose is a determiner, or possessive adjective (two names for the same thing).

She's a talented young girl who IS also a teacher
= a talented young girl who's also a teacher

You know that it must be 'who's' because there is an object, a teacher. The article 'a' is a giveaway too; "whose" the possessive is never followed by an article.
You can be a teacher (who IS a teacher, is, from to be, she is). But 'whose' wouldn't make sense here.

'whose' just means 'OF the person I just mentionned.

The girl whose teacher I just spoke to.
I just spoke to the girl's teacher, the teacher of the girl.

:) Good luck

if you can replace who's by who is, it is correct.

She is a young talented girl who is also a teacher--correct

it would be "who's" because "whose" is possessive which would not work in that sentence

Who's. It means "Who is".

Also, it is spelled sentence not "sentense".

It would be who's.

she is not posessing anything if she is 'also a good teacher', so it is who's