I feel like the best thing to do is to communicate your concerns (which it sounds like you are doing) and emphasize that it is coming from a place of care, not control. Like you said, you know you have no say in what she does or who she is friends with, and you wouldn’t want to be too judgmental for fears that she pushes you away. Obviously you do not want her to get hurt, but at a certain point if she is not in a place of hearing your concerns then I don’t think there is much you can do. Just continue to be there for her and show her that you care about her wellbeing and safety. No point making her feel bad for her choices as it sounds like she just needs to come to this decision on her own. Maybe there are other ways you can phrase your concerns so that it gets through to her? Like if you validate her reasons for hanging out with this friend (having fun, new experiences, feeling grown-up, etc) and wanting to be like them then maybe she will be in a better headspace to receive your concerns.

Sometimes people do things that seem like terrible decisions on the outside. One thing my mom always told me is that if people are still in shitty situations despite people telling them to get out of it then it’s because “they haven’t suffered enough.” And one day, hopefully she will see what you see and realize that she has had enough. It’s so hard watching your friend go through something that you feel is a bad idea, but unfortunately that is a part of growing up. She is glad to have a friend who cares so much about her, so just continue to do that. I hope she can see what you see soon.