Rihanna seems to adore Beyonce. It is Beyonce who seems rather icy toward her. Her "Some artists care about their hairstyle" remark as well as "People don't make albums anymore, they put these quick little singles then they burn out" comment were pretty shady.
Basically. Rihanna puts out better material than her with less talent and I am sure deep down that bothers her. Rihanna is her karma for her hogging the spotlight and doing the other Destinys Child members wrong.