For those interested, Smash Bros. was datamined some time ago. Joker's character was usually defined as "Jack," but there was an alternate version "Jane" with a ponytail.
Should lend some more credence to this being the femprotag, because I know there is a lot of debate.
Also, her character design is indicative of a main character. There would be more alterations to her uniform if she was just going to be the prerequisite Aeon arcana.