I still think it must be a mink.
Inu and Neko are basically out. They've suffered way too much and their fight against Jack would've made no sense at all.
Carrot is 100% out, too. She wasn't even alive 20 years ago.
The other minks simply aren't impactful enough. Nobody would care for the traitor if it was one of the musketeers or Wanda (heck, I bet many weekly readers would have to look up who that character is again).