Baby sisters Little Sisters 1 by Katy Farina

Karen Brewer lives next door to Mrs. Porter, who wears long robes and has wild gray hair. Mrs. Porter has a black cat named Midnight and always seems to be working in her garden. Karen is not supposed to spy on her neighbor, but she is 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!