The novel is set in London, however the setting was changed to New York in order to make it connect with an American audience and as New York was seen as a selling point to female audiences following the success of Sex and the City (1998).
Kristin Scott Thomas revealed in 2014 that she disliked the experience of filming; "I thought it would be quite good fun. But I spent my entire time waiting. I hated it, hated it, hated it, and I said that I wouldn't do another one. Funnily enough, I haven't been asked to."
Isla Fisher researched shopaholism by visiting some overspend/under earner groups, who essentially are shopaholics and whose lives have essentially become unmanageable because of their shopping addiction.
The trivia item below may give away important plot points.
At the end, Rebecca pays off her entire debt in coins, stating that she was doing it in the most inconvenient way possible. In real life, Mr. Smeath could have refused to accept it. While coins are legal tender within the Federal Reserve System, no law requires a merchant or anyone else to accept them. Legally, however, the debt would be considered paid off if he'd refused her payment.