Karen's Witch - Baby-Sitters Little Sister Graphic Novels #1 by Ann M. Martin

Karen Brewer lives next door to Mrs. Porter, who wears long black robes and has wild gray hair. Mrs. Porter has a black cat named Midnight and always seems to be working in her garden. Karen isn't supposed to spy on her neighbor, but she's determined to prove that Mrs. Porter is a witch named Morbidda Destiny!

Mrs. Porter is getting ready to have a special meeting at her house, and Karen is sure the meeting is for witches. Are they going to cast a spell on Karen? Or will she be brave enough to send them away -- once and for all?