How can i get sweet revenge on an ex-friend?

Im 16 and my best friend totally changed this year of high school.(im in 11th gr), I never drink, and she has started drinking all the time and is "popular" now and is nice to my face, but she is soo rude behind my back. I dont ever go out of my way to talk to her, but if i happen to see her in the hall or something i am always nice! so i dont get why she suddenly doesnt like me so much! On facebook she removed me from her top friends, when i used to be #1! and now she has even added me as a limited friend so even if i wanted to talk to her, i couldnt! I have made new friends and I try not to let her rudeness bother me, but im a very sensitive girl and im upset and want her to get a taste of what a jerk she has been! I happen to know her parents would ground her for eternity if they knew she parties all the time! is there a way i cud secretly rat her out, or should i just stay out of it??!