It's strange how one flop single can make a person lose so much momentum. It's like the GP wants nothing to do with a flop. But then again, they latched on to Work. I'm clueless...
Which flop single though? The only real flop single she has is Put Your Hearts Up and she hates it herself. Rihanna has released 8 albums and cemented herself as pop force and beside what @Truth Teller said which I agree with, we also live in a time where basically every current active pop act that debuted in the last 5 years has to fight with every single release. One succesful global era doesn't guarantee that every song is gonna blast off to the highs of the charts. She has not lost any momentum, she does more than fine.