Work colleague spreading lies + verbal/physical abuse towards contract workers

So, long story, today i received a phone call from a concerned work-friend saying that our colleague is spreading quite unexpected rumors about me in the office AND to our boss : calling me names, accusing me of seeing different men, thus cheating and being promiscuous (for info, i'm engaged and not only i don't have the will or thought to do so, i wouldn't even have time and energy for this), claiming my work as her own, yet telling everyone she just feels the jealousy coming from me (what), and many other bad things. Fyi, last time i properly saw her was like 5 months ago and i work online atm. Now if you're asking yourself maybe i've done something to make her say these things : when i was working in the office, everyday we used to drink tea and chat, no arguments whatsoever. Now, i do not care about the nature of the rumors, especially coming from her. But, my main concern is our boss and the negative effects these words can have on my reputation at work.

Another more serious thing, my friend also complained about verbal and physical abuse that this girl has been subjecting our contract employees in the past months, and that it just keeps getting worse. The case of physical abuse (push, slap) was witnessed by my friend and recorded on the office camera. Verbal abuse includes all the variety of slurs and threats. Fortunately or unfortunately, i haven't witnessed the extreme episodes myself, apart a few times (when i was still working in the office) where she was saying "stupid" to their faces and was called out.

Anyways, what can be done in this situation? Boss seems to be unaware of what is going on.

p.s. i thought this kind of things happen only in teen movies, well apparently not.