"Of course I'll save you," Hazel said earnestly, "but not now."
Since Madeline knew this, if Hazel released Madeline, maybe Madeline would obstruct what Joshua and Simon wanted to do.
Since Simon was so defensive against Madeline, perhaps the family behind Madeline did have the strength to scare them. Hazel wasn't stupid enough to do anything that would hold them back, so she couldn't let Madeline go now.
"You, you lied to me!" Madeline was so furious that even her eyes turned red.
"I'm not going to lie to you," Hazel said dryly. "When I'm ready, I'll definitely come here to save you."
Madeline didn't believe her. She couldn't help swearing at Hazel with every dirty word that she could think of.