The 22-year-old Barbadian beauty is good friends with the singer and she was seen attending her bachelorette party in Las Vegas last month.
Asked if she is going to the wedding, she said to Entertainment Tonight: "I am going. It is in India. I am excited about that because I have never been there. I am just excited to see her get married.
"I am excited to see her dress. She won't tell me what it is."
The pair became good friends when they were sat together at an awards show and Rihanna added that they get on really well.
She said: "From there, she just seemed to be a down-to-earth person. In the industry, you don't meet a lot of people who are genuine and you can always tell when it is a face that they put on.
"It is okay. I get it. With Katy, she is just such a free spirit. She has no edit button at all."