"friend" will not stop following me?

[315]

okay so last year i was new to the school and while on a walk we bumped into these neighbours (2 doors down) and started talking. my mum found out about this school and she decided to send me there. on the first day my neighbour seeming nice and all introduced me to her "best friend" and so we became a group of 3.
the first term was good i was being to feel accepted by these kids and felt i belonged there. in term 2 things started to go down hill.
this girl i sat next to in music that was partly in my group told me they (lets call her M) was i huge ***** and that i shouldn't hang out with her etc.
i found i new group with more of the people in my classes and became part of their group and then M was ditched by her best friend because she had had enough of her back stabbing and general rudeness. so the M started to follow me around at lunch times and recess and still continues to follow me around like a lost puppy. that was last year and more **** happened since but i only have 500 character left soooo...
any way i have tried to ignore her but she keeps texting my and stuff. so today i went to the movies with my close friends and her twin and then i started to get bitchy messages from her saying I'm unpopular and should get many likes on instagram and such so i replied with the help of my friends with snappy comebacks and she took forever to reply.
she is still texting me and is really getting on my nerves what should i do?
(btw its school holidays)