[matese]

I am going to stretch real far on this thought, since you never checked the webcam at the pet resort you don't don't if she played with other dogs, if she did, maybe this is what she misses, playmates. If you requested that she not be allowed around other dogs, then that theory is out. If you don't know if she was with other dogs perhaps you could call the resort and ask.
or
Being away from you for an entire week she could have thought you abandoned her. Stress can knock ppl out, has the same affect on dogs. You wrote she looked a bit thinner but the amount of left over dog food look correct, that's telling you she didn't eat well for the time she was away from you. I agree with Maximo, give her a week, if you see no improvement it's vet time.
One last thing, never think you are asking to many questions, there would be no YT if ppl didn't ask, and, for every question asked and answered at least one person will gain knowledge from it.