I think 'bunch' of flowers should be accepted.
'Bouquet' is used in England for a formal bunch of flowers, such as might be carried by a bride, or presented to a musician or actor after an admired performance. Otherwise 'bunch' is used
What's wrong with "Pauline n'a jamais payée..." since pauline is feminine
You change the endings with auxiliary ÊTRE, not with AVOIR
I typed "Pauline never paid for one single bouquet of flowers" and am unclear why that would be incorrect. It is along the lines of "not even one bouquet". If I am wrong, how would one say that Pauline had never paid for one bouquet?
Pauline HAS never paid for a bouquet of flowers
"Pauline has never paid for a single bouquet of flowers" is a literal translation and should be accepted.