Makeba Riddick is a singer-songwriter who has been active since 2005. She is originally from West Baltimore, Maryland, US. Currently she is managed by Jay-Z's record label and production house, Roc Nation.
She's worked with both Beyonce and Rihanna in the past
Edit: Maybe Nikita/Riddick/Victoria wrote a new verse for Rih and maybe something for them to sing together? And that's the reason the original Blow writers aren't credited