We are told early in the book that Mig is named after Aunt Maria's "daughter who died"; Naomi actually did not die, but was turned into a wolf -- by her own mother -- immediately after imprisoning Antony Green.
Only Aunt Maria, Naomi, and Antony Green himself knew what had become of him; his sudden disappearance apparently drove his mother mad. However, there is a more chilling possibility; Aunt Maria, telling Mig that her magic begins "with talk" which enables mind-control, says, "I wish you could have been there when I had my long talk with poor Zoe Green. That was me at my best." It is possible, as Mig suspects, that Aunt Maria deliberately drove Zoe Green mad.
The cat which so angers Aunt Maria, and which Betty Laker adopts and names "Lavinia" after the absent companion, is actually Lavinia herself. Although Antony Green attempts to change her back into human form, Lavinia wishes to stay a cat, and does, becoming Betty Laker's pet.
Betty Laker and Antony Green marry at the end of the book.