At some point Pinkie asks Sunset how long has she been on the time loop. Sunset's answer? "Happy birthday", implying that it was at least a year.
Sunset can pass from just discovering that there's a time loop and telling the Equestria Girls what's the problem to predicting things the reader might not have experienced. Plus, some moments can be interpreted as Sunset losing the notion of time. With the confirmation of her on the RV ending and the good ending she has been trying for a year, it means that Sunset already experienced events that the reader hasn't the moment she discovers the time loop.
