The singer - whose new album Unapologetic is due out today (Monday, November 19) - has been flying fans and reporters around the world on a specially-chartered plane, and is visiting seven countries in the space of seven days for gigs and public appearances.
"Rihanna delays going on stage, which throws out the whole schedule," an insider is quoted as telling The Sun. "It's a reaction to the fact that every second of her time is accounted for by organisers. She likes to be in control.
"Her team have been making frantic calls throughout the night to the airports. Every hour that goes by she has to pay for flight clearance on runways, and also incurs costs of the private airport teams, customs, baggage handlers and security. The tour will end up costing her a fortune."
Rihanna will switch on the Christmas lights at Westfield Stratford City in East London at 5pm today.
It was reported last month that Westfield bosses were prepared to pay the star as much as £5 million ($7.96 million) to secure her appearance.
Watch Rihanna's music video for 'Diamonds' below:
Photo gallery - Rihanna performs at Victoria's Secret fashion show:
Copyright: Rex Features Startraks Photo/Rex Features