hey mimi..aww thats really sad..i guess u don live in India?!..bcuz its really rare here..so i've never known anyone who has gone through this..
so i think u shud just try n act normal with her, forget that shegot into this. Its gonna be hard but u hafta try..n maybe she MISSES you..so she will come back to normal eventually..
n i dont think its a phase..does'nt happen to everyone...maybe she went through something bad which she cudnt share?!..maybe its depression..idk..bcuz normally ppl will go into alchohol and drugs only if dey're depressed abt smtn..or hate their life.
it could also be bad influence..but u hafta try n talk to other ppl who know her and try to make her feel loved..so she stays away from her BF and other bad company..
Hope it helped :)
-aish