Rihanna HAS sold 100m+ singles in the U.S if you count her features. If you want a number that has her U.S single sales as a lead artist it was
75.9M as of March 30 2015 according to Billboard. Since then FFS, BBHMM, and AO have sold ~2m (FFS had been out for a month by then) so it's safe to estimate Rihanna's U.S single sales as a lead artist at 78M.
Now if you add
Love The Way You Lie (6.4M)
Live Your Life (4.7M)
The Monster (3.8M)
Run This Town (3.5M)
Take Care (1.6M)
Fly (1.5M)
You arrive to 78M + 21.5M featured singles =
99.5M singles sold in the U.S including featured. Add on her flop features like CRTFY, Who's That Chick, and All of The Lights that I cannot find sales for and you will comfortably surpass 100M.