She did never did anything THAT bad.
1) The Riona situation. Quinn didn't tell her about the possible risks and lied when she said everything was under control. We know what that led to.
2) Quinn continues to lie to Sage and use her, although Sage considers her her best friend.
3) Quinn gets people hooked on drugs (like Karen). And don't tell me that they are adults and make their own choices.
Drugs are addictive and they take away a person's ability to think straight. Quinn knows this and takes advantage of it.
4) If it weren't for Quinn, Mona would never have dropped out of college (I'll never forgive her for that).
5) Quinn is constantly deceiving people for money. For example, she sells Dave counterfeit pills. I don't care about alphas, but honestly, if he found out the truth and broke Quinn's jaw, he would be 100% right.
6) As far as I know, Quinn still hasn't told the MC that Vinny's gun was real.
7) The game doesn't directly confirm this, but I think we all understand that Quinn was going to blackmail Maya into joining the restaurant.