For legal recourse? It depends on a great many things, and you'd need a local lawyer to tell you. It's possible that you can sue this individual on libel, for example. Regardless, pursuing any sort of legal recourse is likely to be a long and highly unpleasant affair. It is significantly less likely that you'd have legal recourse against the company, especially if they're being hired into a position that would not interact meaningfully with you. That's what you'd need to actually apply leverage to the company itself.
Beyond that, this stinks of office politics. The staff member was fired for gross misconduct and now has been hired back. That's the sort of thing that requires significant ability to influence people. Most likely, she was either able to convince the owner to take her back directly or convince one of the people just below the owner to intercede on her behalf. Trying to interfere with that in a controlled way is going to require throwing around some pretty potent office politics of your own, and if you were good at that, you wouldn't be coming to the internet to figure out how to do it.
Still, even so, you're not entirely without recourse. You were a legitimately wronged and threatened party. You can at least express concern. Let go of "not being taken seriously". You have my sympathy on that one, and it sucks, but it's not going to help you in the face of the sort of mojo that can get someone re-hired after "fired for gross misconduct".
The best response I can come up with... pick the highest tier of the company that you can get one-on-one time with, and request a meeting with them through whatever methods your company has. It sounds like, for you, that goes as high as the owner. Be respectful. Express that you are concerned. You heard that this person was being allowed back into the company after she nearly ruined your career with false accusations. The last you saw of them, they were cussing you out to your face. They apparently have enough pull to get re-hired in spite of being fired for cause. These are legitimate sources of concern. Unfortunately, this is seriously unlikely to make any real changes right now. You'll get reassured, but it won't go anywhere - and the correct way to respond is to simply accept those reassurances. If you had the pull to get her kicked out now they would have talked with you before bringing her in. On the other hand, it will leave her on rather thinner ice overall. The owner will have made reassurances, after all. He's unlikely to appreciate being made a liar if she ever comes after you later.
If that's not good enough, then you're going to have to play office politics a little harder yourself. You'll need someone who is not you, who didn't make the decision to bring her back in, who values you enough to go to bat for you, who can get the ear of the owner relatively readily, and who was more important to the overall company structure than she was. Having them be in your chain of command would help. Go to that person with your concerns, and see if you can get them to go to bat for you. In cases like this, having someone else arguing on your behalf is a lot stronger than trying to do it for yourself. Of course, it requires that there be someone like that who values you that much. Having them be personally offended by the false accusations might help as well.
Of course, you could also just walk. If "leave the company and find a better one" is a viable option for you, you might want to seriously consider leaving the company and finding a better one... and you'll have a heck of an answer for the "why did you leave your last workplace" question.
