What's happening with this?

[Snavey4xx]

There's this girl on twitter who is friend's with one of my best friend's. She's been saying some rude things behind my back, calling me a liar, a b****, saying I'm not a decent person. This has been going on for about 2 or 3 months. So lately I've been really upset because my best friend was planning to commit..err..suicide;(. So I posted on twitter 'I hope you're happy..' about the person who drove her to want to commit suicide. Well..later my friend told me to look on the girls (my best friends friends) twitter, so I did and it said things like 'Yes, Im happy, as long as you're miserable, I am very, very happy' and then later she put 'probably wasnt even about me, but as long as someones making you unhappy, its good enough for me'. Later I found out she's always looking on my twitter..that she always has a tab up of my twitter on her laptop. I was upset enough as it was, she made me a whole lot worse. She's actually the reason I started cutting, something that I regret..She's horrible. I don't know what's happening though..I don't know what I should do if it carries on. I've told my friends and they say its cyber-bullying but I'm not sure..