Dog I'm sitting for a week keeps growling at me?

I haven't had a dog growl at me, but I always assess during the M&G how the dog responds to me as well as my dog, who pretty much ignores/tolerates most of my guests. I once had a dog that was very skittish, She wouldn't allow me to get near her; she would run behind her owner. Treats didn't work either. I did not feel confident I could ever get close enough to put her leash on. So the owner and I decided that this was not going to work.

As for your current situation, just leave the door to the crate open and allow the dog to come out on its own. Don't try to force things. Leave its food outside, if possible, and see if it will approach you.

Talk to the owner, if possible, to see if they have any advice.

I agree with the previous answer. First thing to do is communicate to the owner what’s happening and ask if they have any tips. The emphasis needs to be that you’re trying to create a Safe & happy stay for the dog. Usually, walking with a dog is bonding time. However, this dog sounds like it could be a flight risk. I also agree that you don’t want to force things and leave the crate door open.

Sounds like this dog is stressed out by the boarding experience. I’d nicely suggest to the owner that unless there’s something medically going on that’s causing her behavior to be different, this dog might be most comfortable staying at home with either housesitting or walk/drop in services for future stays.