My friend is addicted

My best friend who I’ve known since I was 3 has recently became a smoking addict, marijuana and tobacco. She’s 16. She only tried it around April this year just to see what its like and I don’t think she expected this to happen. She smokes almost everyday, whenever she has an opportunity she’ll take it. I can see how negatively it’s affecting her life but she’s in denial. Every time I tell her how bad it is she’s like “yeah I know” and makes excuses but she doesn’t do anything to try stop. she used to be such a committed rower and would spend her time training but she quit, she barely comes to school, she doesn’t come out with her friends because she’d rather stay home and smoke and she’s failing almost every subject in school. Her parents are completely clueless. It’s honestly heartbreaking seeing her like this and I don’t know what to do to help, I don’t want to rat her out but she needs help😭