Well, it's partly because Lizzy tells them all that Edith was part of the kidnapping as well ,that's why she wasn't with them as hostage...and they alle believe her, but no Killian ...at least that's what happened in the book,maybe they are going to change it? The mother is already changing.. ┑( ̄Д  ̄)┍
Spoiler
Well it's like spoiling the end...hmm...what I can say is, since they had Edith on another place and Lizzy and the duchess in another room (way better than a torturous basement like Edith btw :/) when the OG male lead aka Cliff comes to the rescue ,he doesn't even look after Edith when Lizzy tells him that Edith was in on it, since that crazy maid hears that, she plays along and tell them that it was all her mistress idea or something like that,they kill everyone who is there and go without looking for poor Edith whom was tortured so bad that her face it's a mess and she can barely walk, the only reason she gets away from there is because she gets to talk to the guy that was hired (yk the one at the end of the chapter, that asked for her relationship with his employer) she gives him her necklace and he loses her ropes,and she tells him to get out of there because soon it will be a blodbad...he lament that all he can do is that...and leaves..the reason she got away of the basement was because the maid was about to kill her but cliff came and she left to help without locking the door ,thinking Edith was still unable to get away from the ropes and will die anyways...

Ugh, what I heard about the torture that Edith goes through is bad. And Cliff still blames her for all of it