Plus-que-parfait vs imparfait

Hi Paul, 

Could you let me know which writing exercise this refers to or the context ?

Hi Cécile, It is the May 25 Writing Challenge, Level B1: Trip to Paris

Kwiziq does not allow me to do the challenge more than once so I cannot show you the English sentence, but I think it was "She'd been dreaming of it (the trip) for ever, and the given translation is "Elle en rêvait depuis toujours."

Thanks, Paul