Queen of babble / Meg Cabot.

Enhanced descriptions from Syndetics:

Lizzie Nichols has a problem: she can't keep anything to herself. And when she opens her big mouth on a trip to London, her good intentions get her long-distance beau, Andrew, in major hot water. Now she's stuck in England with no boyfriend and no place to stay until the departure date on her nonrefundable airline ticket. Fortunately, Lizzie's best friend and college roommate, Shari, is spending her summer catering weddings in a sixteenth-century château in southern France. Who cares if Lizzie's never traveled alone in her life and only speaks rudimentary French? She's off to Souillac to lend a helping hand!

One glimpse of gorgeous Château Mirac--and of gorgeous Luke, the son of the château's owner--and Lizzie's smitten. But thanks to her chronic inability to keep a secret, before the first cork has been popped Luke hates her, the bride is in tears, and Château Mirac is on the road to becoming a lipo-recovery spa. Add to that the arrival of ex-beau Andrew, who's looking for "closure" (or at least a loan), and everything--including Lizzie's shot at true love--is in la toilette . . . unless she can figure out some way to use her big mouth to save the day.