As far as the religious order abbreviation of Mary Floradora is concerned, arg is German for bad but that doesn’t mean much (bad Mary?).
Dido most likely refers to the founder and first Queen of Carthage (in modern-day Tunisia). She is best known from the account given by the Roman poet Virgil in his Aeneid. The name Dido, used mostly by Latin writers, seems to be a Phoenician form meaning "wanderer". She was also the subject of a short play by Christopher Marlowe.