I was bullied by someone who I thought was my friend

I became quick friends with this girl in 6th grade. Her and I were very close friends. December of 6th grade I started getting mean notes and it turned out to be that friend. Then later in February of that school year she stole my ice cream gift card that I won in a raffle. After all of that I had to stop being friends with her. She bullied me even more after I stopped being friends with her. She sent me a mean email threatening me to my school email. She sent a mean email about me to one of my friends behind my back.