Here is the original item:
Citing writer's block as the reason
(A) that
she did not have her essay,
(B) Yao received
no sympathy from Professor Santos.
(C) Who will
only accept "breather's block" as a legitimate excuse for
late work.
You wanted to do this:
Citing writer's block as the reason,
that she did not have her essay, Yao
received no sympathy from Professor Santos. Who will only accept "breather's
block" as a legitimate excuse for late work.
Adding a comma after reason not only is incorrect but also fails to fix the fragment that still exists. You need to reconsider your options!
You might want to review the rules.