Where are people getting that Ahsoka "knows" about Anakin and Padme? From her final line where she says "I know" after Anakin confesses to having feelings of wanting to leave the Jedi? That doesn't quite seal it for me.
It's not just her line, it's the surprised and guilty expression on Anakin's face in response to her line. Well, maybe not "guilty," but the kind of look someone gets on his face when he realizes that someone else knows a secret he's been keeping. That's what told me she was talking about him and Padme.