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 drove Zoe Green mad.