This is an important page to read on that subject - not only does the Ringmaster frown on fighting with murderous intent in the carnival, it's against one of the three rules, and is usually punished in a fairly eye for an eye manner. That is, if you make a serious attempt on another carnival worker's life, then it is entirely possible (and actually likely) that she'll kill you. Context has some bearing of course, but the equivalent of 3rd degree murder (that is, planning a murder in advance ) would be the most likely to receive corporal punishment, or a transfiguration equivalent.

She considers killing her workers to be stealing from her, which is one of the gravest offenses you can make against a fae like her. Fighting and general violence isn't as big of a deal provided you weren't clearly going for the kill, so long as you're not making things difficult for the carnival. Her attachment to her workers is largely sentimental, and if they prove themselves a detriment then she doesn't consider herself to be losing much from violently ending them.

There are no specific rules against killing people who aren't from the carnival, and so the general rule of thumb is that if you aren't causing trouble or ruining business, then its probably okay.