When they come over, instead of having to always tell the what DD can do (in other words, having to stick your head in the living room every five minutes to head them off), why not just tell them what she can't do? Since she's well-behaved, there's probably only two or three behaviors they need to watch out for in the amount of time they will be seeing her. So you could say something like,
"Oh, just a head's up! DD is not allowed to set the cat on fire or pawn the TV, but anything else is fine. Thanks!"
Then, if you hear them scold her, you can pop in and say, "Oh no, was DD trying to pawn the TV again?" And if they say no, she was trying to set up a lemonade stand, then you can smile and say in a friendly, puzzled voice: "Oh, DD is not allowed to set the cat on fire or pawn the TV, but everything else is fine. Thanks!" (Yes, repeat the exact same phrase.)