Smoothie's power should make her a great counter to fishmen, merfolks and their water-based martial arts such as Fishman Karate, Jujutsu or Merman Combat with her draining the water they project or manipulate and inside them if she grabs or slash them with her blade.
I wouldn't be surprised if her sword can also takes the properties of liquids it absorbs like the juice coming from lava rocks could possibly turns her sword into a lava one or poison.