Mandil can sometimes be found halfway across Cyrodiil at The Count's Arms in Anvil on the 5th and 6th of every month. She is a member of the Thieves Guild. Mandil can be located in the Imperial City Market District during the afternoon hours except on Sundas, when she frequents the Arboretum.
Imperial City: "It pays to know about locks and lockpicks. It's just a hobby, of course, but the average citizen feels more secure when he understands his own locks."