No, Rihanna's music has always followed trends set before her. That is why she's so popular. She has never and will most likely never do anything different that could cause a riff in the mainstream music scene.
She has set more style trends than she has music trends. But i must say I love what she has done for pop especially meshing reggae influences in her music. Rihanna has some really great and diverse songs. If you really think about it, she is one of the very rare black artists who isnt R&B but still is successful. Sonically, she has great songs but it would be nice if vocally she was just as refined.
Why do people say she follows trends when she's one of the more riskier pop girls? Not many pop girls would be released a dark ballad such as Russian Roulette as a first single which went against the sound of the radio at that point in time.