"And have you a grandmother?"
"My Nana, yes, my father's mother. I usually call her on Fridays," she added, realizing with a guilty start that today was Friday and that Nana Newman would be expecting a call.
"Every Friday," the Witch of Endor said significantly, and looked at Scatty again, but the Warrior deliberately turned away and concentrated on an ornate glass paperweight. (36.21-23)
The Witch of Endor is asking a rather sneaky, double-edged question. On one hand, she is interrogating Sophie about whether she calls her grandmother (which makes Sophie feel guilty because she loves her grandmother very much and has not called), and on the other hand, she is trying to make Scatty feel guilty for not calling her own grandmother (the Witch, herself). She's one tough cookie.