Restac wasn't a fool, contrary to popular belief. She wasn't about to do anything that'd cost herself or her sister any more freedoms... they'd been through too much for that. She'd seen her sister dead, after all.
That kind of reaction from the ape was quite surprising. Freeing them both would've been a mistake at any other time, but not... Restac found it rather hard to even consider going up to exact her revenge. There were more important things in this very room.