help?

It's this female in my grade (9th) and she keeps wishing death on me and my boyfriend, and talk about me and all that. The reason why is because my boyfriend is her ex and she just hates to see him happy. Me and him tell eachother don't entertain it but she keeps coming back! I know if I go tell an adult I'll be labeled as "scary" or a "snitch" . I can fight, I just don't choose to. I have a lot going myself to mess it up with a fight. I also know if I say stuff back, she'll make it bigger than what it is and have all of her friends doing the same she is doing. And me, being a lonely freshman with no friends, can't go against that. What should I do?