Astropath and Navigator are the most useful archtypes, though Missionary or Sister of Battle would also come in handy.  I would also allow her to play an Imperial Psyker using the rules from Black Crusade (which is basically an xp advancement chart that can be explained very quickly)   Such a psyker would have fate points as a normal Imperial character, but wouldn't advance in a career, buying psychic powers from Rogue Trader, Black Crusade, and adapting powers from Dark Heresy as appropriate.<br/><br/>I have Inquisitor and Sister of Battle written up as Rogue Trader classes, if someone wants to play them, so it wouldn't be hard to work in, if someone wanted to play them.  I would probably request an Ordo Malleus inquisitor, though.  I would also allow an assassin, scholar, or bureaucract who uses the rules from Black Crusade.  (A Black Crusade based character is much easier to balance in Rogue Trader than a Dark Heresy character, but might be a lot harder for a first time player because one has to pick and choose what they want)