I know I love Quinn, it's actually fucking hilarious how she lives in the head of so many that actively 'hate her', marks of a great character. And Sally is akin to a 'loli tsundere fantasy', so yeah.
Or those people 'hating' her also are morally bankrupt but push their holier-than-thou act to the utmost, whatever.
Does she do reprehensible acts ? Obviously.
Does her past explains her actions ? Of course it does.
Can she be redeemed ? I hope so, but I'm not sure it's possible, she'll have to face the music at some point anyway, or if it's possible, I hope it's well-written cause it wouldn't make sense if it just 'happens'.
Now, hating a character that much, da fuck, get a hold on your life