If you cast
Olivia, Mobilized for War, and your opponent exiles it with
Spell Queller, and then you play another Olivia, assuming she resolves, your're good to go. Since the one in
exile isn't on the battlefield, nothing of note occurs.
However, if you were to attack with Olivia and they blocked on their
Spell Queller, the Queller would die and your old Olivia would return to the battlefield. At this point the Legend rule would apply and one of the two Olvias (I Believe of your choice) would go to your graveyard.
Hope that answers your question