Charlotte wasn't crazy and Miriam's dress.
I think she was just 'damaged' traumatized from the tragedy. and became a recluse
to escape. when she was talking to Harry on the grounds she was very realistic in her conversation with him. the fact she was now in doubt about her own sanity proves she was sane ( and not evil like Drew and Miriam)
because of Miriam's vindictive jealousy and vicious black mailing Jewell and Charlotte were the real victims in the ordeal. Look how quickly Drew conspired with Miriam ( though it's unclear WHEN he joined forces with Miriam) Poor Charlotte never stood a chance! but WHO did slash that dress!??