This is an unseen character who was married to Vlad Demonic.  When Frank meets him for the first time in the boiler rooms, Vlad tells him that she and their children were killed when Austria took Bosnia, which is coroborated by Sasha Barbicon.

Unseen Characters
Annie Morrow | Charles | Duke of Norwick | Enid | Emily Troutt | George Quincy Clifford | Isidor Straus | Landlady | Matthew Morrow | Tom | T.S.D. Hipple | Vlad Demonic's children | Vlad Demonic's wife | W.E. Carter