Enemy
It wasn't that Sylas didn't understand Professor Fembroise. She felt like her government had abandoned her, so what reason did she have to remain loyal?
But this wasn't how Sylas saw things. He didn't care if she betrayed the Terranova government. However, foolishly betraying Earth and siding with their invaders was something that he couldn't allow. That was because her help would inevitably harm him and his own chances in the future.
If he had sensed that there was a chance to change her mind, he would have taken it. But, their relationship had already been harmed by how long it took Sylas to return. And, the hatred in her heart had only grown since the last time Sylas had seen her.
Although it seemed like Sylas was just willing to allow anyone with talent into his fold, he actually had a standard of trustworthiness that had to be met first.