I agree that you did the right thing. These people are adults, right?! What adult spits in someone's coke? I haven't heard of crap like that since I was in seventh grade. Give me a break. If she gets fired, it's her own damn fault for being such an idiot. BTW, you didn't start anything -- Cindy did, so don't feel bad.
As for the others, just keep your distance from them as best you can, and don't leave any food or drinks near them...