My younger sister is doing drugs - HELP!

Hi everybody.
I love my sister to death and I would really appreciate your help. Any help means a lot.
I have a younger sister (I'm going to be next month 25 and she's going to be 22 this year). She went to a neighbour country (we're in Europe) 2 years ago where she's studying acting – she's very talented and knows how to work. She is a very good, intelligent, bright and unique individual. She's been there for two years and she comes back every 3 months for a week and every summer for 2 months. We have a very good relationship, we're very honest with each other, we both have goals in life and so on. We also have a very good relationship with our parents, altough they are divorced. Our mom has depression and she'll sometimes go into a dark place (we all do though) but not like too much or whatever, but I guess she's more prone to bad thoughts sometimes altough she is a positive person, if that makes sense.
When she was 16 she was going through a rough time (puberty, problems with mom etc) and I found out she did coke a couple of times. We had a deep talk and this is where our relationship started to grow and it's been solid like a rock since then. I decided to not tell the parents and she stopped doing drugs – I know that for a fact, no doubt about it.
She's been smoking weed through high school and college but I know about that, I used to smoke weed from time to time. She works hard at college, doing everything on time but she'll smoke a joint before going to sleep – her habit in order to relax from a stressful day etc. – I know it's not the best thing in the world but it is what it is and I don't think weed is all that bed if you have certain things handled altough if it would be up to me I would of course like her to stop.
But that's not the problem.
I just found out from her best friend that now she's also doing seruizs drugs – I think mostly mdma, and some coke too. She'll do that once or twice a month, maybe once every three weeks.
Basically so many people on her acting college do that it's unbealivable, everybody. So she kind of fell into that. Plus she's kind of messing around with a guy (on and off) who also does drugs, more then her I think. She's coming back home for the summer for two months.
I know I'll talk with her about that but I don't know what to say... should I give her gentle advice, seriously confront her, just listen to her to find out more, tell our parents (dad is very strict).
How is this situation the most efficiently solved and how to stop her from doing that?
Thanks so much, appreciate it!
Asked Jun 09, 2016
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Answered Aug 25, 2018

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