This might be less about trusting strangers and more about being defensive about criticism from family, and merely pointing to someone who does not disagree with her as validation.
I don't know enough about the communications dynamic in your family, but if most of your interactions with her are of the "you are young and foolish, you need to listen to me," then she might be reacting to feeling dismissed, and latching onto anything that shows that she's her own person.
Even if you have the wisdom and experience, and her decisions are clearly not carefully considered, you have to find a way to get her to see that, from her own perspective, or she will (if this is a factor) reject it out of hand as being critical of her, not trying to help.
This means you have to listen, very, very carefully. Let her express her needs, why she feels the need to do what she does, and understand what she might be looking for from you. You need to put yourself firmly in her shoes, and see things from her perspective (does not automatically mean you agree), and communicate to her in a way that she understands that you appreciate where she is coming from.
Once you have that common ground, then you can explore, from her point of view, the reasons and consequences for her actions, and find alternatives, or, at least, a different method, that can address whatever it is she seems to be thinking she is getting from her choices, but in a more healthy, mutually beneficial fashion.
It is pretty late to the game, and it's not going to be easy, but you need to understand it's not something you are going to be able to impose, by your own force of will. The two of you have to get there together, which will probably mean more listening and less telling than you are probably used to.
Even if this were not the case, it's a tough age where they are undergoing rapid changes, physically and emotionally. They want to be adults, but really don't understand the scope of the responsibilities that come with that freedom. Because they don't truly understand it, they feel frustrated at not being given free reign to do as they please. But the time will come, soon enough, that it will all be on them, so, as parents, we need to be there to help with that transition, and we need to help make that transition happen by giving more and more of that freedom and responsibility, over time.