It is a tough situation, and like yourself I hate seeing pets kept in conditions like that. However, do keep in mind that we all love our pets in different ways. Obviously the dog seemed happy and cared for prior to you dropping the dog off at home. Even though her house may be a mess and the dogs area is not the way you would have it does not mean that the owner does not show her dog love once she gets home. (after all, she did call and pay for a dog sitter).
Another way you can look at it, is it kind of like clients that crate their dogs. Its not for me, I let my dog have free run of the house. He gets to decided where he wants to take his naps (on the bed or the couch) what room he wants to hang out in or if he wants to look out the window when I am not home. Where other dog owners put their dogs in crates and keep them locked up all day. Crating a dog is not for me or my dog but it doesn't make my way any better than the client who crates their dogs. We all have different life styles and degrees in which we take care (spoil) our pets.
What I have done in the past is when seeing a dog left outside with it raining and no shelter, no toys (and this was a puppy), the only area the dog had to lye on was the dirt or on a cardboard box the owner put out on the cement) What I did was brought the dog a blanket to lye on, and brought over some toys (old toys and some from the dollar store) for her to play with. I building a shelter with the cardboard box and two fordable chairs that were outside. The owner got the idea and the next week when I went over there, they had bought her a little dog house.
If in any way the pets ever seem as if they are being hurt or the owner is not getting the pet medical care when needed at that point I would call animal control. Other wise I remind myself that we all have different ways of showing our love and affection to our pets.
Hope this helped!