Huh. Like a lot of other people, I always thought it was 'Hey'.
But now you're all saying she mouthes two syllables in the video? (I'm too lazy to actually watch the video, due to a slow internet connection, but I'll take your word for it)
i always thought she said "oh hey"
most plausible answer, I reckon. It gets in the two syllable thing, and means that I am half-right.
Awesome!