HELP ME PLEASE REALLLLLLLY ANNOYING GIRL WHO WONT LEAVE ME ALONE!!!!!!!!!!!!!!!!!!!!!!!!!… HELP!!!!!!?

Before i was born my mom met one of her best friends Pam My mom got pregnant with me and then Pam got pregnant with her daughter Melanie when i was growing up me and melanie kind of went our own ways. I made friends and she did not. When my mom asked me when i was about 7 to invite her to play with me and my friends because she had none i agreed. As soon as we got there she turned into a huge jerk and told me my friends were mean and she hated them. i told her to go home and i told my mom never to invite her over again. Then in the summer of 4th grade she still had no friends but she considered us best friends even though i tried to make it clear i did not like her so she called MY MOM and asked HER if we cud hang out all summer my mom knew i didn't want to so she said we'll call you. we never called her. Then melanie made friends with a few people and basked in the glory of having friends she told everybody she new that didnt go to our school she has more friends then me and made it seem like i was a loser. When i tried to be nice to her she acted like she was better than me. Then at the 8th grade she had a HUGE fallout with her so called friends and came to me asking to sit at my lunch tabel and be her best friends shes sooo annoying and thinks she knows more than me PLUS all my friends cannot stand her! and our parents are not even friends anymore what shud i do??? I also cant just ditch her because shes in my Dance Cl and i have to see her twice a week not to mention in school then one time i told her i didnt like her she told her mom and everybody else making me seem like abitch! then she called my mom again sobbing and my mom got mad at me!!! its not fair UGH what shud i do?!!