My friend turned on me because I refused to watch her be mean to someone else. Advice?

Give yourself some credit, at least you took the higher road and apologized even when you didn't need to, you also asked her to stop getting people involved; and from my perspective, she's just an immature little girl wanting attention. She puts other people down to make herself look like she's top notch or some s.h.i.t! If you're smart, you wouldn't fall for it. Simply ignore her until she just stops, eventually she'll become bored with picking at everybody else's flaws because she knows nobody really gives a damn. Act as if you don't care. Or say, "Dana, you're lame, you're really going to just sit there and waste 10 minutes of your life talking and ranting about people you suposably don't like, well guess what, nobody cares and nobody ever cared, your best bet is to shut the hell up now before all your friends turn on you like you did to me." Just tell her how it is. The truth is hard to swallow, if she's as 'tough ***' as she seems to be, then she should handle the truth like a man and suck it up. The things you said were also NOT "unforgivable" so what, you spoke your mind and she couldn't take it. Sorry hun, but "best-friends" don't judge their bestfriends so quickly, let alone even just turn on them for other people. Tell her to lay off. She's nobody.