Walk up and take her pipe away
I've been thinking about doing this the next time a white, fake "pipe carrier" crosses my path. The thing is, it would not be as clear-cut if I took the pipe away from them, being a white person myself. If I did take the pipe away from them, I assume they would fight me somehow; maybe call the police. If it was at a public event, I think a white person doing this to another white person would need some kind of backup, like, "I am taking this and sending it to this First Nations group so they can decide what to do with it."
There would probably also need to be some precedents to cite if it went to court. I avoid these newage types as much as possible these days, but there are some that turn up... One, a few years ago, claimed the chanupa she had was borrowed from someone Lakota. I was so stunned she had it, and was planning on using it, I didn't know what to do. But now I'm thinking about what would be best if and when the situation arises again. I'm also thinking about how best to handle it if their use of the pipe has not been made completely public, even if a number of people know what they are up to.