What should I do?

I wanna preface this by saying I have no problem with drinking or drugs or people who do these. This is about my friend who I’m worried about. It may come across as such, but it’s because I’m worried about the effect they are having on her. This may be long but here goes: In school me and a girl became best friends. At 15, a new girl joined and became friend with us. This friend was a bad influence, drugs, stealing, drinking. My friend started doing these things, but the other friend left a year later and neither of us stayed in contact. My friend phased out of that stuff. Then 6 form happened. The friend became very different: drinking, manic. But this was only around certain people. When it was just us she was fine, and even admitted to doing these things to fit in with other people. I explained she didn’t need too, and that if people expect you or want you to do drugs then they are bad people. But then we found a bag of ❄️❄️ in a bathroom and she just did it. I was trying to tell her no and it could be laced. She ended up passing out and I freaked out so much, thinking she’d overdosed or been poisened. This caused a shadow over our friendship, and we stopped talking. She didnt really care about this. I tried explaining the dangers of drugs, but she didn’t care. She then went to university. Her flatmates are heavy drinkers and drug users. We met up 2 times since she started, and when it’s just us it’s fine, she says how it annoyed her that they drink and do drugs, but then posts pictures on social media and she is high and drunk in all of them. The issue is that over the last few months, these posts and stories (we talk sometimes and she tells me stories) having been getting more frequent and more intense. I’m worried she’s spiralling or an addict or something. I’ve tried messaging a few times but no reply at all. I remember at school we were best friends, and she was super smart and very well behaved. I was even jealous at how smart she was. She’s admitted to doing these things to fit in and not seem like an annoying roommate, but I’m worried she’s in the wrong crowd or something. She’s not replying at all and only posts drinking and party things. What should I do? If you want any more information pls ask away. There’s so many more things to add but I wanna get the main stuff out. I’m also so sorry at how long this is.