Ugh! so many posts, can't take it all in...................my 15 year old in this situation(which she would NEVER be allowed in) would be strictly instructed that if I should hear that anything negative or inappropriate happened during my absence, I'd have her hide on a stick. Me being the dog sitter, I WOULD report all issues that were inappropriate and let the parents decide if and what to do about it. I would NOT be sleeping there to supervise any 16 year old who clearly has an opinion of her own as to proper behaviour.
No worries here though, my job is to be the mama to all my girls, I would never place anyone in such a stressful position. I have a dog and if I'm going to be away for a week's time, girls come with me, or they go to a friend's and dog is either boarded with a friend or reputatable establishment.
Totally unfair to put you in this spot!!!