The `Rude Boy' singer - who is close friends with the `Teenage Dream' hitmaker and organised her recent bachelorette party in Las Vegas - has revealed she is very well prepared for Katy and her fiance Russell Brand's nuptials, which are set to take place in India in the coming weeks.
She said: "I'm going to wear Stella McCartney and Topshop, of course!"
Rihanna also revealed Katy has been talking so much about her big day she has put her off getting wed anytime soon.
The 22-year-old pop star - who is dating Los Angeles Dodgers baseball star Matt Kemp - added: "I've heard the word marriage 400 times in the past few days. I'm not ready for that yet myself."
Rihanna has had an eventful career and personal life since she rose to fame as a teenager. She has released five albums and was the victim of domestic abuse at the hands of her ex-boyfriend Chris Brown - who beat her up in his car in February 2009.
But the singer is adamant she didn't miss out on enjoying her youth.
She said in an interview with Britain's OK! magazine: "I was always mature for my age. I enjoy knowledge, so I hang out with a lot of older people - I always have."
Rihanna also believes that good can come from bad situations.
She explained: "In life, every negative that happens leads to something great - you just can't see it at the time. I wouldn't be the woman I am today without the bad things that have happened to me. My skin wouldn't be this thick and you need that in this industry."