Spoiler warning for Rebels.
This is about when Ahsoka was working with the Rebellion, not after Rebels.
In the Ahsoka novel, there is a brief scene where Ahsoka hears Bail talking to a young Leia. This is around the time Ahsoka tells Bail that she's going to join the Rebellion. This book takes place, according to Wookieepedia, one year after the events of Revenge of the Sith.
In Rebels, we learn about how Ahsoka is helping the Rebellion, and we also see how Leia is as well, working with her father, Bail. Given that the two both worked with the Rebellion and with Bail Organa, is there any evidence that they ever met? Ahsoka wouldn't have known about Leia's true parentage, but she could've known her simply as another Rebel and as Bail's daughter.