Ms Kerris also defended the current pricing structure as parallel to Apple's mobile software store.
"Just as we have allowed developers to set prices on the App Store, publishers set prices on the iBookstore," she said.
The US Department of Justice (DoJ) is suing the technology giant for allegedly breaching antitrust laws with five major book publishers – HarperCollins, Hachette, Penguin Group, Macmillan and Simon & Schuster.
According to DoJ filings lodged in a Manhattan Court, in September 2008 and January 2009 the chief executives of the five publishers met for a series of dinners in a private room at an upmarket New York restaurant, where they are alleged to have discussed "business matters".
On a separate occasion, they met with a sixth publisher, again in a private dining room, where the DoJ claims they "discussed the growth of e-books and complained about Amazon's role in that growth".
Not long after, in 2010, the five publishers accused of colluding with Apple signed up to the so-called "agency model" of pricing, under which they dictate the price of an ebook as long as they give 30pc of the revenues to the retailer.
"Publishers saw the rise on e-books, and particularly Amazon's price discounting, as a substantial challenge to their traditional business model [and] feared that lower retail prices for e-books might lead eventually to lower wholesale prices for e-books [and] lower prices for print books," the DoJ said. To combat this, they "teamed up with Apple, which shared the same goal of restraining retail price competition", it added.
