I believe DC took her daughter and hid her from CP. Something damaging was either going on with MC (or about to start) initiated by CP. Perhaps SA. And DC took her daughter and put her in a safe place.
I think CP's quick trip to MI was to look for MC after he demanded to know where the girl was; perhaps DC told him that's where she sent her daughter to put him off track. And is why he asked her was she hiding MC from him. Because MC would be able to tell what he had done or was going to do. I think that plywood room was going to be for MC, and with no outsiders ever visiting, who would know about it other than DC? DC as a mother might choose to hide her daughter from her husband and be jailed rather than reveal what happened and give CP a chance to go after her if he made bail and she did not or could not. With her daughter safe, she doesn't have to say a thing.