How do I deal with a co-worker making harmful allegations at new job?

Is this the only job available to you? Because honestly, this is not someone with whom you should be working (or being friends or hanging out or being in the same room), and it seems to me that the easiest course of action is for you to find another job. Seriously: stop worrying about who's right or what's fair, and avoid the drama that your having any sort of relationship with this person will inevitably bring.

Calling her a psychopath and a compulsive liar is calling her an insulting name. Since you did it by text I imagine she has evidence to show if it is her word vs yours. I don't expect that the company will be big fans of you both. I would go in calmly and if they ask you about it state that you had past differences and it won't affect your work once again and be prepared to be let go. Also don't send people you work with insulting texts especially in a small community like the restaurant business.

Oh and as an employer, if I saw a text saying someone was saying a sociopath and a compulsive liar, I would actually more question the receiver than the sender. The text could very well be true, there's no reason for a third party to think she's the victim.I would think that it showed exceptionally poor judgment to, upon realizing that a friend was a sociopath and a compulsive liar, send that friend a text saying that she was a sociopath and a liar. When dealing with sociopaths, the best course of action is to back away slowly, not to escalate by sending insulting text messages. It doesn't sound like either of these people is someone whom I would want to hire: she's unhinged, and he doesn't have the sense to avoid unhinged people. Now seems like a good time for him to develop that sort of good sense and perhaps to reflect on why he pursued a friendship with someone who had previously assaulted him with a traffic cone.

Bill Cosby used to say "Parents aren't interested in justice. They want quiet." You could surprise me, but most restaurant mgmt isn't going to want to "hear testimony" or read old texts or play Judge Judy. It'll probably be more like Person A makes a complaint about Person B to mgmt. Mgmt will talk briefly to Person B, and then decide to fire one of them. With that in mind, think about how Person B might impress mgmt as the better employee, long-term.

I have never harmed, threatened, or even called this woman an insulting name, despite the chaos that has surrounded us. Chaos doesn't just "surround" people. Accept that you are an active participant in this volatile relationship. The fact that she resorted to physical violence doesn't absolve you of blame, or make her concerns about working with you any less valid. In fact, she's probably correct to not want to work with you, although she obviously should have never encouraged you to apply in the first place. If you still do want the job though, you need to appear to be as drama-free as possible. This means not going into details about past events, speaking in broad terms that don't blame one party more than another, and avoiding being alone with her. Don't talk to her unless it's about work, and don't talk to her at all unless someone else is in the room. This still might not work-- it really depends on who the management likes more or who is a better employee.

Your course of action should be to look for another job. What you should expect is that your ass is going to be fired eventually because you make your coworker feel unsafe and uncomfortable. Even if this is the best job ever, do you really want to go to work every day and deal with this drama? Go work somewhere with people who don't hit you with traffic cones.

I have never harmed, threatened, or even called this woman an insulting name, despite the chaos that has surrounded us. Calling someone a sociopath and a compulsive liar is calling them an insulting name. You did this by text, so she has written evidence of your bad behavior. I suggest that whatever you do, you should not lie to your boss like you lied in your question. Your best course of action is to behave as professionally as possible, tell your new boss that you'll be professional, and never have contact with your frenemy again. And in the future, contact the police when someone assaults you so you have a paper trail.

I feel as if they would have no right to fire me, since this is a he-said, she-said situation, Are you in america? If so, then they most likely do have the right to fire you even if they did not list "unknown new employees causing drama" in their set of known fireable offences.

I think you need to do three things. The first thing is to go into work and be the most professional you can be. Turn up early, go and find the boss, etc. Show an interest in the workplace and ask if there are any policies you should be aware of. Do your job really well and basically be a model employee. The next thing to do is to cut as many tie to this woman as possible. Anyone who will attack you with a traffic cone (!) is someone to run the hell away from. That is completely unacceptable behaviour, and what is more worrying to me is rather than her getting away from you, she's enmeshing herself with you even more. Consider why someone who felt it necessary to treat you so badly is encouraging you to get a job working alongside her - perhaps it's because she can cause more trouble. Proximity to this person seems to cause you a lot of that. The final thing to do is consider your own part in all of this. There are two sides to every story and it's on you to take ownership of the fact that you ignored a massive red flag, and then continues to associate with someone you think is a sociopath and a compulsive liar. Her behaviour is unacceptable, but yours isn't fantastic either. For your own sake, have a think about why you're putting yourself in this situation all over again.