River City Girls 2

This achievement is unlocked by story progression and is unlocked by beating the boss of the Flatiron district.

You should use a character that had a decent XP level. i used Misako at level 18. It was a pretty easy fight, but it gets quite hectic with tarot cards flying around at some moment. At these bits stay in the middle to avoid auto selecting cards that are unfavorable to you. It could trigger all sorts of things like zombie hordes and more. Resist trying to hit her when she spawns near you after that, as she will be invulnerable and whoop your butt. Just stay away and let her do her thing and avoid the enchanted D20s and kill the occasional zombie. She has a cooldown period when she's vulnerable. That's your time to attack. Three well placed combo's was all it took to take her out.