She's certainly qualified to simply state "you know, whenever I am unsure of something, I like to talk to my parents" or something along those lines.
This isn't about parents rights, this is about parents duties. This is their duty. They need to take care of their kid, they don't need to have some kid acting as her confidant.
I don't know what you find so bad about merely suggesting she talk to her parents.
And again, this behavior may potentially lead to the parents separating the two if they can't trust the 16 year old. This isn't a threat or something I am saying they should do, but its something they might well do and then the poor girl loses a friend and someone she trust.
Your poor advice has consequences, remember that.