My thinking is this.. he promised her something. "If you shut up, I'll let you go once we get money out of the ATM in awhile" or something like that. Or it was a threat, where he said he'd shoot her if she said a word. She was trying to be "good" and not get hurt, thinking she'd get away or he'd let her get away eventually. I mean, those scenarios have happened many times in the past. :-/
The LE saying they aren't sure if this is a criminal case yet (I forget their exact wording) is what makes me wonder. Overall I feel she was taken against her will, but a small part of me wonders.. maybe so the chance of her still being alive is a good possibility.
JMO.