I would've...

Given that you were relatively alone... (see my own GMs too - I wasn't) although I would've stopped her, as that was the most "responsible" thing to do, it wouldn't have been without a vocal response too. Something like "you know, you're not supposed to do that". I would try to make her understand that it's not wrong what she was feeling, but not appropriate either to act upon it, given the climate around the world these days. That way it's not like you're saying "go away" but still you stay in the prison cell which is outside (not inside) the bars... She will not like it, but will appreciate that you didn't just say "no, stupid child" but gave her a person-like response...