Psychic dampener
From Jenny Everywhere Wiki
Wendy VII owned a psychic dampener resembling a hair-clip, given to her by the Mother Superior of the Sisterhood of the Holy Snail two weeks ago. She once explained that it made her “completely invisible to all spiritual methods of detection — including a disembodied spirit’s very senses”. This notably made her invisible to Wraiths. (PROSE: The Time of the Toymaker)