I'd say 300xp would be appropriate for Pilot (Walker) as an elite advance, since it's an in theme Void Mistress core skill.  Sarah can pick it up at any time she has a week or so to train on how to operate walkers properly.<br/><br/>Also, I would be perfectly happy with having Sarah strap on the armor from a regular armsman or an elite armsman.  (she could even keep the equipment, though it would probably annoy whoever she took it from)