The 56-year-old actress and television personality said on Wednesday's episode of Watch What Happens Live that she's unsure if Richards will show up at the reunion following her drama with the group.
"Well, what I will say is I'll believe it when I see it. When I see everybody at that reunion I'll be like, okay," Rinna said.
Richards stopped filming the show in December, sparking reports she was quitting the Bravo series.
"She didn't show up to some things," Rinna confirmed. "She told me she was going to be at something that she didn't come to, so how can I know for sure?"
"I'm sure she's going to be there, but you know, anything can happen," she said of the reunion. "I'll believe it when I see it."
Richards said on WWHL this month that her friendship with Rinna has changed since they clashed in Season 10.
"There's definitely been a change in our friendship. You know, people will see that as the show plays out," Richards said. "We've been friends, though, for over 20 years and we never know what's going to happen in life. So, we'll see."
During Wednesday's episode, Rinna also played a game where she answered whether she regrets some of her memorable moments on Real Housewives of Beverly Hills.
Rinna said she regrets confronting her former co-star Yolanda Hadid about possibly having Munchausen syndrome but doesn't regret letting Kim Richards anger her to the point of smashing a wine glass or giving Richards the infamous bunny.