There was only a little truth to what she was saying. Yes, she believed that they needed to keep a close watch on Rabastan, but she didn't actually want to return to the scene of her crime because of the future Dark Lord's ascension battle. She wanted to see what was happening down in Level Eleven. Surely someone knew by then that there was an escaped prisoner? If she didn't make it seem as if she was at least interested in what was happening, it might come back to bite her. Guilty people ran. She didn't want to run just yet. Not until she knew whether or not she'd been successful in returning Aberforth to the Resistance. She was still vulnerable otherwise.