Well, if she's thrown to the ground, she'll have trouble escaping the destruction of the Lamps.
Of course, we didn't stipulate this, but there is no reason she couldn't necessarily come with them to the Lamps, but arrives with the intent of stopping them.
What we're setting up here is that this is not an easy choice for her. She was one of those fanatical supporters of Melkor who comes with him to Arda. We're also setting up a more interesting setpiece than a "No-Holds Barred Beatdown" by the entire staff of the Balrogs.