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Sally is a member of her school's gardening club.

I would like to confirm whether it is correct to replace "school's" with 'school'?
Comments  
Yes, either is fine.
Would you write:
Sally is a member of her club.
?

I wouldn't. The club isn't hers, it's school's, or it's every member's club.
Same with:
Sally is a member of her school gardening club.

But I would write:
Sally is a member of the club.
Sally is a member of the school gardening club.
Students: Are you brave enough to let our tutors analyse your pronunciation?
If she is a member, it is automatically her club; there is nothing wrong with the originals in my estimation. Sally can even be President of her club.
I think so Mr.Hancu

you're right..
Mister MicawberIf she is a member, it is automatically her club; there is nothing wrong with the originals in my estimation. Sally can even be President of her club.
I agree with
President of her club.
but one is member of "his/her" club by definition once he/she is in it, thus to me
member of her club
sounds redundant to me.
Teachers: We supply a list of EFL job vacancies
but it meant her school's gardening club. That sounds fine to me. Otherwise you don't know that it is the club at her school. If you just say 'the school's..' she might not be a student there.
BTW, IMO the original sentence is fine.