Which means that it's not written in stone, which suggests they don't know "the future" but just what might happen. It sounds as if that could have been a prediction based on what's known (by a ghost, who has better supernatural information than the rest of us) to be happening in the present. I wouldn't know. I'm guessing that was pre-Barnabas. I'm not saying you're wrong; I'm just trying to be conservative about it.
[Very spoilery]
I think an example of Sarah's precognition occurs later in ep #344, when she appears (though only her flute playing is heard) to tell David of an imminent catastrophic event that has no basis in current events:
DAVID: Do you hear that?
CAROLYN: Yes.
DAVID: It's Sarah! Something's going to happen! Soon, very soon!
CAROLYN: What?
DAVID: Nobody knows it yet, but it's going to happen far, far away.
CAROLYN: Where?
DAVID: No one knows yet, but it's going to make us all very sad for a long time. No one's going to cause it, and no one can stop it. It's going to be an accident.
CAROLYN: Who's it going to happen to?
DAVID: Nobody knows yet.
CAROLYN: David, none of this is real. It can't be!
DAVID: It is, and there's nothing we can do about it. Nothing.
In the next scene, David bids goodbye to Burke.