Do I have the right to punish her?

I am guardian of my four younger siblings who are minors. The oldest one is seventeen, although we never really had the kind of relationship. She always helped me raise the younger ones, and I always gave her freedom. Now, though, she went to a party where the teens got drunk. I told her no more parties because I didn't want her to get drunk, again. Then, I caught her trying to sneak out. I told her she was grounded, but then she told me that I have no right to punish her because I'm not her father. Is she right? Or do I have the right to punish her?