What can I do if there is a friend doing duster at my house?

i have a 4 yr old and my wife has a friend duster'ing pur say, didn't know about this till I caught my wife doing it. as well I dont know what to do I want her to stop and she sais i can stop when im ready,...and then she stumbles into the room with her right arm all drawn up.i dont want to loose our son in the process but i dont want her doing it! mostly cause i dont want to loose her!