Can you tell me if I should be worried about this dog?

I am house and dog sitting for three dogs – two boxers and a mutt. The youngest boxer bitch, 2 years old if I remember correctly, has just recently started acting strangely. I have been here for six days, and just last night, she started dry heaving sporadically. It sounded like she was about to throw up a hair ball, but nothing ever came out. She has began drinking a lot of water, but only from the water dish that is outside and, if she can get access to it, the toilet. She does not drink from the water dish inside. She also, for the first time, refused to eat. She was very defensive, however, when the other boxer tried to get at her bowl. She did eat a dog treat earlier in the day, though. She seems to be more depressed than she has been, but still gets excited from time to time. Does anyone have an idea of what, if anything, is wrong? Does she just miss her owners and the behaviors are just now surfacing? Should I be worried about her? Is there something I can do for her?

**Edit: It has also just started storming, as of a few minutes ago, and she has been pacing around some. I also just gave her a dog treat, and she ate that, but she, once again, turned down food.