Lisa apologised, the reason for her keeping it a secret from him was because she understood Chuck's character the most. Once he realises that he was saved and that too by a Demon noble, a race that they considered as their enemy, he would be disheartened and it might even leave a shadow that he cannot come out from.
Even if it made her a little cruel to keep him away from the truth, she didn't want the talent of her man, his shine to diminish like that. Lisa though that she could keep it a secret from him; however when she heard that Chuck was taken along with Godwin and the others to hunt down the demon noble who was responsible for saving them, she couldn't keep herself out of it.
"W-Why are you telling this to me now?"