This is an unlikely match, but The Companions By Sheri Tepper, involves a woman who steps through a portal to another planet where humans are used as beasts of burdens for an alien species that are dog shaped. These dog like aliens are not at all like real dogs. Instead they are cruel and self centered. That part of the story is only about a 4th of the whole plot which explores humans and other species and our dominant/subordinant relationships with eachother. The young woman travels the universe, ostensibly as an assistant to her brother, an inter-species communicator, but really as a spy for one of the political parties here on Earth. Eventually she does escape the dog aliens and flies off on a space ship with a number of people, including love interests.