Rewriting this sentence

(1)As subject of a relative clause which restricts the meaning of a noun,that is used more often than which in informal English eg:-
The sc, (of which she is head), is closing.
=The sc.that is head for her...

(2)In relative clauses that add information but do not restrict the meaning of what comes before, you usually use which, especially after a comma:-eg:-
The sc., (head of which she is), is closing.
=She is head, which is "of which"..is unclear.

I see. Thank you for your opinion.

第一句不能改成第二句。第二句句子是不確的。

還原第一句成為未合併前的情況：
The school is closing. She is the head of the school.

'which' 是 'the school' 的 relative pronoun. 但通常在合併過程中， prep 'of' 會跟著 relative pronoun 在一起，所以就變成了你的第一句。