Yeah-I wasn't sure if it definitely meant that she was going, which is why I included ????'s in my title. But it does sound like it may be true. The picture was clearly labeled as "farewell dinner", so there wouldn't really be any other context for that.
I'm just taking a guess, but my guess would be that it's related to her recent trip to Korea/Japan and the apparently huge success they've had with their songs over there. Who knows...maybe she'll move more into song writing, maybe she's got some sort of her own deal in the works, matbe she's ready to start a family....who knows. Life on the road is really tough though.
I've liked all of Carrie's bgv's, but Jamie REALLY blended well with Carrie, so it'll be sad to see her go. Assuming this is true though, I'm sure they already have someone lined up.
Edited to add: I see more comments on the picture, which includes one from the wife of one of the guitar players (Shawn) who says something to the effect that it won't be the same without Jamie. Bummer.