Of course she could go on to become someone bigger, but she still has a ways to go. She's on a right enough track, but I have my reasons for not trusting what I see from her now as something that will last or reach something that Beyonce has created for herself.
There's nothing particularly novel about Rihanna as a talent or personality that makes me think that she'll use what she has to keep on going. She only strikes me as a pretty girl with a decent voice who lucked out by having the most talented management team and production clan in the business currently. To me she seems to have garnered capital, success and reach through the talents and merits of the people behind the curtain (which is why I compare her to Britney Spears a lot). You can see it in ALL of her songs. Every single one of her successful singles become huge because they were well-written, well-produced, and thus highly played. They weren't successful only because she sang them. Yes, the snowball effect that happened after her success with GGGB made it so that her name on a single meant higher sales, I'm not disputing that. But it doesn't take away from the fact that at the ROOT of everything is a woman who is generally unremarkable. I might even slightly believe that she'll reach a status like Beyonce in 10 years, but a much bigger part of me doesn't want her to because I don't think she's worthy of it.
I can think of so many people right now in pop who, if given the same resources and team that Rihanna has, could truly take things to the next level musically. I don't think she has the creativity, vision, or raw talent to see it through.