I found condoms and sexy toys in my sister's backpack

So, accidently, while searching for her pencil case, because I wanted to borrow a pen, I found out a pencil case full of condoms and those dice with s3x positions you can find on Tyger and Ale-hop.

I'm the oldest sister of a very large family, she's the second child. She just turned 18, half a month ago. We are a catholic christian family and our parents always taught us with christian principles, which included wanting for marriage and not having s3x just for pleasure. I personally am very connected with the church and I want to follow those principles because I think they are the best for me. On the other hand, my sister, even though she goes to church (most times she doesn't go with us, but to another mass with her friends), always seemed to me like it wasn't something that important in her life. I do also know she and her boyfriend used to send spicy pictures to each other and masturbate themselves while on a call. So I’ve known for a long time that she doesn’t  want to live her life that way God taught us through the Bible.

I don't know what to do now. I know it's her life and I don't get to choose what she does, but, at the same time, I'm very concerned about her and I don't want her to commit a mistake she can't undo (that is presuming she isn't having s3x yet). If I talk to her she won't probably listen and will leave the room without letting me finish or will start screaming at me. I know she is having a tough time in school.

What should I do? Should I try to ask her, even though she will probably get mad at me? Should I tell my parents? Am I being too judgemental?

(I apologize for any mistakes, english is not my first language)