The most common and most likely answer to this crossword clue is the 5 plus 1 plus 5 plus 3 letter word CARRY A TORCH FOR
I've seen this crossword clue in The Daily Telegraph
C
A
R
R
Y
A
T
O
R
C
H
F
O
R
Buddy explains!
The straight part
We know that "What usherette must do because of love without response" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what usherette must do because of love without response = carry a torch for.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.