"I heard rumours that Rhianna was going to take over the reins of Discworld."
They're not rumours. Pterry announced three years ago that he was leaving the reins to her. However, she doesn't feel that she could do his work justice in the form of novels and will be restricting herself to Discworld projects In other media: scripts for the Watch TV series and a Wee Free Men movie are in development.
(Given her background in computer games ... how about a Discworld MMO?)