Just theorizing, but her powers answered the question why the kids couldn't just overpower her and escape just like that (or make a break for it after Rahne half-mauled her); since she kept the facility under a force field, they couldn't just slip out the back door and were forced to confront her again after the charade was revealed. Also, given that she's a heroic character in the source material, that might've helped set up the surprise of her being a villain in this one.
Seems logical.