Castelia didn't know Maddie was thinking that hard until she said it. If have to be honest, Maddie said, "I want to solve this problem without betraying Melody. I don't want to say it, but we put her in that position, but she forgave us after you left Joshua when she could have burned and dumped us without anyone noticing. Even if I had to choose, I'd rather kill Joshua than betray Maddie."
The only reason Maddie backed down was because Castelia loved Joshua so much. Melody and Maddie thought things were over after Castelia and Joshua split up but who would have thought the story would be so different than they expected?
"You keep saying us, but you know I'm the one in the wrong," muttered Castelia, thinking it would be better if Maddie said her name in person than sharing the blame considering Maddie had done nothing wrong.