Addressed by who, though, Nika? Her friends? Bella herself?
And true, Bella talks fondly of Nika both if she's fooling around with him or if she's in friendly terms with him (Haven't tested a playthrough where he threats her, though). Bella suffers from what I call the 'beaten dog syndrome': A dog that has been abused in the past will bark and sometimes even bite any human that approaches them after they're rescued, and it takes some time for them to heal enough to overcome the trauma and allow contact.
I don't believe she's a true psycopath, cause we can see different scenarios where she feels empathy and compassion (Like you mentioned, feeling bad about Brenda, feeling protective of her shorty rude friend, recognizing and complimenting people when she knows they're nice, caring about Nika after his fight with Sai, reassuring him that taking therapy with her mum will help him, etc).
But sadly, people know her for her outbursts and how her behavior changed (the beaten dog) after Melanie Ceril bullied her, cause there's when she started to viciously attack people like Mila in such way that people started to recognize her for that, and that's why Jeff warns us about her. Hell, she gets so mad at you over such a small thing that she ends up hurting Nika during a match, and even her own mum thought she had beaten Nika and immediately scolded her.