I took that as nothing more than KC's sarcastic, angry reaction to her mother's statement which not only didn't proclaim her belief in KC's innocence, it actually implied that KC might somehow be covering up her actual involvement in Caylee's disappearance. To me, KC's comeback was simply the equivalent of "I can't believe you said that, what the hell were you thinking!" or "Are you trying to help me or hurt me?" Or, closer to the point, "With friends like you, I don't need any enemies, mother!"
KC's reaction here was one of the minute # of times her words have actually seemed normal and approproiate to me."