I’d also be annoyed (as a tattooed mother of a tattooed daughter, no less — although she waited until she was 26 to get one), because of the undermining of a specific parental rule, but... they’re teenagers.

The 19-yr-old had to know it wasn’t okay with the parents, because she masqueraded as a guardian (which wouldn’t have been necessary, with parental consent.) I can’t see a way in which the 16-yr-old could have *deceived* her into doing it.

But, yeah, the natural consequences are grounding for the daughter, telling the aunt that you’re disappointed and don’t plan on giving them unsupervised time away from the house together for a while, and then let it go.