Here is the item again:
As all of her classmates were sharing
results (A)
Melody quietly left the room
(B) and found
a quiet corner in the hallway
(C) so that
she could see her grade without embarrassing herself in front of her friends.
You correctly realized that a comma after results was needed. To fix the problem, you chose to do this:
As all of her classmates were sharing results,
Melody quietly left the room and found a quiet corner in the hallway
so that she could see her grade without embarrassing herself in front of
her friends.
As all of her classmates were sharing results is a subordinate clause. It must be correctly attached to the main clause that follows. You correctly employed Punctuation Rule 2:
Subordinate Clause + , + Main Clause.
Excellent choice!