Sounds like it's time for you to step back and for her to start experiencing natural consequences.
She gets a belly piercing that goes wrong - instead of trying to help (which she doesn't want), you say, "Oh dear. What are you going to do about it?" She organises the GP appointment, which doesn't go well, and then she might ask you for your advice about what to do next.
She's going to an event at a certain place, and isn't ready 20 minutes before it starts, but you know it takes 20 minutes to get there. You say nothing and let her be late. If it's your event too, you tell her that you're leaving at 20 minutes to, because you know how long it takes to get there and don't want to be late. If she's not ready, she doesn't come.
It sounds like it's a bit of a combination between her being a stroppy teenager and you liking to have your say about everything rather than leaving people to work things out for themselves.
The response to "You don't always have to be right" is "'Always' and 'never' aren't helpful or realistic ways of looking at the world. In this instance, I think '[insert your opinion here]'. You obviously see things differently, but I suspect that view might not give you the results you're after. Happy to be proven wrong, though!"