>>2962828>>2962843>>2962856>>2962880She's the monstergirl who fills the niche of the vulnerable and invalid monstergirl who always needs somebody to help her (at least outside the water). Also, yes, she has a little bit bigger role in the manga and what bothers me about the anime is that they left out the hint of her character development.
Also, for some reason, she's quite popular with the female fans