how to get this girl to stop bothering me?

I am a 25 year old guy studying bachelors for a year now and there's this girl in my class. she is 19 years old. we first started talking when we were both put in the same group for a class project. I was studying and also working in my uni at that time. she started asking me about my job at uni, how I got it and also asked personal questions. I didn't think much of it at the time and thought maybe she is trying to be friendly. then, I asked her one day if she wanted to go clubbing with me and she said sure but with other classmates with us. then she suddenly started showing interest towards me and I told her that I liked her and she turned me down and said she is not ready for relationships. Later, she started dating someone and didn't tell me for a while until I found out about it. she started asking me more about my job and I was getting annoyed so I changed the topic every time. 4 months later, she started working in my office at uni and suddenly her behaviour changed towards me. she started behaving more rudely, making backhanded compliments and always argued with me whenever we talked. once we had an argument in texts and she posted it on her instagram so I stopped talking to her. but she didn't stop there. she turned everyone, who was working with us, against me and even told them that I am chasing her and everyone started behaving differently towards me. finally, I have left me job and am only a student there, still don't know what to do about her.