You're looking at this from the wrong angle. A DM sent to girlgeeks will be delivered to girlgeeks, exactly as the sender specified... much in the same way that

You're looking at this from the wrong angle. A DM sent to girlgeeks will be delivered to girlgeeks, exactly as the sender specified... much in the same way that a postal carrier will deliver private snail mail to a street address even if the intended recipient has already moved. Unlike snail mail where you can address a specific individual by name (thus making it illegal for someone else to open it) Twitter is the equivalent of "Dear Occupant" and whoever is at that address can open it.