Factory-ship-produced variant of the Sabre will be your main craft during early missions of Act II. After ItDW it replaced Encantona as main fighter of The Fleet. And yes, you will also utilize her atmospheric flight capabilities.
As for the prequel, there is started script for Exile: Origins - mini campaign prequen spin-off set during initial days of ORS rebellion with Harper as main protag. It has very low priprity at this moment.