In the washroom of Relucia Diner Bella says some really awful and immensely hurtful things to Brenda Vosolovo in order to distract her and to give the MC enough time to copy data from her smartphone.
And an upset and tearful Ms Vosolovo reacts by saying, "And- and you! You're the-e last one who-" which could be interpreted in several ways, e.g., Bella had an affair with an older married man which hurt people collaterally and did a lot of damage.
Or could Ms Vosolovo be referencing heartbreak caused to Bella when her own father, Amber's husband, began an illicit affair with a younger woman and ruined the family as a result? Maybe Bella's father left Amber and Bella for a much younger woman taking Bella's beloved sister with him, possibly going abroad to a country beyond their reach, and refusing spitefully to give Amber/Bella access to said daughter/sister estranging the two girls permanently. If the father happened to be a really malicious and nasty piece of work he might even have tried to play one sister off against the other, deliberately poisoning Bella'a sister against Bella and Amber until their relationships crumbled and the sisters were forced to take different sides, loyal to one parent and hostile to the other, painfully and comprehensively alienating the sisters one from the other despite them having been loving siblings in a happy nuclear family.
Would a tragedy like that be bad enough to wreck Bella's life enough to leave her psychically burned, scarred and damaged enough to explain why she behaves in the way that she does? Bella showed genuine remorse about the way she wounded Brenda Vosolovo and I feel that she is actually a really lovely girl who has been hurt and decided to protect herself afterwards by donning "bitch armour" to keep the world at bay: Bella's strategy seems to be to mock, attack, humiliate and intimidate others in order to deny them the opportunity to get close enough to hurt her, seemingly terrified of developing genuine feelings for anyone, or trusting anyone, or caring about anybody for long enough to drop her barriers and allow somebody, somewhere, somewhen to see the vulnerable, lovely and wonderful young woman she is behind her mask, petrified by the thought of putting herself at risk of suffering more heartbreak and end up shredded and torn apart again if they rejected her, abandoned her or if she lost them for whatever reason.
What clockwork of events could possibly have turned such a shining beauty into such a fierce, aggressive and mistrustful beast? Bella is such a fascinating character that I can't help but muse and wonder what could have happened to have made he so aggressively defensive when I've got twenty minutes leisure to waste like now!