Victor hasn't been to the labyrinth, no, and Pthumeru isn't exactly common knowledge, but most Hunters of the Healing Church will heard of them regardless. I intended to eventually reveal this IC, but after the Night of the Blood Moon Pthumerians have started exiting the labyrinth and causing trouble in and around Yharnam. Victor hasn't seen any Pthumerians personally, but enough Hunters have talked about and described them for him to recognize the signs.

She most likely wouldn't know about Pthumeru (or Pthumerians), but I agree that she might know that some bells can be used for arcane purposes.