friends changing

ok, well one of my good friends that i met in eighth grade was a conservitive jew and a straight "A" student. now in high school she is totally different, she is now doing grugs and drinks constantly. she is hanging out with people that you would never think that she would hang out with. its sad to think that i was her first best friend at her new school, and now she ignores me for these people that are really bad influences to her and she is no longer a straight "A" student, now shes more like a straight "F" student. im scared that she is going to die for overdose or alcohol poisoning.

well my question is should i just let her be like that, or should i talk to her and let her know how i fell. or if you have advice PLEASE HELP ME WITH MY FRIEND PROBLEMS?!!