I just started the 50+ white mage quests, and the #1 reason Ray-o-Senna has you running around doing things is because she is physically unable to leave the Twelveswood. She point blank says it.

Speaking of that, I was always kind of hoping Sylphie might eventually be revealed to be a Padjal. We know she has the talent to be a Hearer already, and she's still young enough.