You are incorrect. Blake does not have a tail. Faunus have 1 animal trait and this is consistent in rwby universe. Blake's animal trait is cat ears. She definitely does not have a tail.
Wiki for reference on the one trait per faunus rule:
https://rwby.fandom.com/wiki/Faunus#:~:text=one%20animalistic%20trait
The only time Blake ever had a tail was in the dream world in the anime spinoff, ice queendom.