What Bree just said is based on what I understood from the map on p.6 of the IC thread.  Hopefully I'm not missing a door that's before the pools - I recall one we tried to open, with painful failure the result.  And since the lower part of the tower is heavily garrisoned, I really don't think we have any choice whatsoever, other than abandoning Aleria again which Bree doesn't wish to do... her "I'm going now" stance is just to spur movement.