Miranda's utterance when waiving to Mlle. de Poitiers

As she waives to Mlle. de Poitiers before going up the rock Miranda makes a single syllable utterance which we cannot hear. I can't say with any confidence what it is, but it seems like "Om", which is of course the chant used in Indian spiritual traditions. On one hand that seems an unlikely thing for an young lady in a strict Victorian era school to utter. On the other hand, given that some people interpret the disappearance of the two girls and the teacher as constituting some kind of spiritual transcendence (rather than them being victims), maybe it's not so outlandish. Perhaps I'm wrong, and perhaps the utterance is of no importance whatsoever, but I'm curious to know what other people think it is.