I would like to hear your opinion as to why exactly you don't like her? Could you give me a more specific reason? We don't have to agree with each other and it's fair that you don't like her, I respect it. I'm just curious and would like to hear your reasoning. Everyone can say they don't like a specific character, but it doesn't mean much without providing something more than "I don't like her/him".
I imagine Derek would turn his back only if you hurt his sister (relationship wise) and even then I feel like it would take a lot of effort to really piss him off for him to consider making such a crucial decision as betraying those closest to him. He has been a good friend all along, just look how hard he tries to cheer MC up. Still I don't think he has it in him to do such a thing no matter what if he truly cares for MC. It wouldn't surprise me if other DIK brothers try to fuck MC over for whatever reason. Feel like that saying "family comes first" is a bit BS.