Get Me Away From Her, Please!!!!

She's always as distant as ever. I've been married to her brother for almost four years now. I've never had any long conversations with her or any of my other in laws. I tend to distant myself due to the fact that I was never perfect and meet up their expectations- be it on cooking, child rearing, and to sum up; everything... I do not value conflicts therefore every time when she made cynical or hurtful remarks about me, i just kept quiet. Deep down inside I always wish that I could get back at her but after thinking them over, I decided not to take any actions out of respect to my MIL.   It was only recently that I feel that I need to break the ice and get to know her and my husband's family better. I have my own social network account and later I discovered that she had just created an account. It took me  sometime to finally contact her via the network.  She responded and she sounded quite decent in the beginning. Things turned out the opposite when she rudely demanded an explanation for my absence on her cousin's wedding. My response to her rude question seemed to ticked her off..That was when I started to see the ugly side of her..From the very day onwards I was the target of her slanderous and malicious statuses...She ridiculed my background and to a certain extent I was extremely affected by her words.. I decided to delete her from my list and I've regained peace but it was not for long. Once, she dropped by at our home with my MIL, her cousins without prior notice..She inspected every inch of my home to find faults and to further spread malicious gossip...She was not successful however...She did not give up few days later I received her friend request and I accepted with the hope that she might have changed. I was totally wrong!!!! During my MIL birthday, I suggested my husband to treat her  (MIL)with a special dinner. She texted my husband telling him that she wanted to tag along.We were very upset with the probability that she may actually ruined the whole dinner. As we picked up my MIL (she and her family stays with my MIL) she came out and knocked on my car window. On our way to the restaurant she texted my husband telling him to do something about me, for not smiling at my MIL. I was accused of being rude to my MIL. She indeed had successfully ruined the whole evening. I did not enjoy the food because I was too sad and angry. The thing did not stop there, she started attacking me with abusive  and rude words, accusing me of not being respectful to my husband and the family. She also put down on my career, my qualification (I have a post graduate degree and working at a reputable institution with steady income) and many other insensible words, quotations on her network status. I guess her main intention is to humiliate me to her list of friends (where majority of them are my husband's relatives). She did many other malicious things and I do not feel like sharing them at the moment.  The things that she did had actually affected my relationship with my husband. We had fights almost every day following her remarks but after sometime I decided to totally ignore her. I did not delete her this time for I do not want to be seen as the losing party.  Most recently, she put up a profile picture of her posing with my favorite blouse... she even sent me countless requests..... I'm so done with getting furious that I do not know how to feel anymore about her. I'm so over done with disgust and hatred towards her that I simply not able to find proper negative adjectives to describe this evil person.