Mush, a Dog From Space — Daniel Pinkwater

LASSIE, GO HOME -- MUSH IS HERE!
Now that Kelly Mangiaro's family has moved out of their apartment into a house, she figures her parents will finally let her get a dog. Instead, her mother gets a job, and Kelly gets a baby-sitter.
Then Kelly comes upon Mush, a mushamute -- a breed not recognized by the Westminster Kennel Club, or by anyone else for that matter, possibly because mushamutes come from the planet Growf-Woof-Woof, in the solar system of Arfturus. Mushamutes can talk, tell time, cook up a storm, and even clean up the kitchen afterwards. Who needs a baby-sitter when there's a mushamute around? Now if only Kelly can persuade her parents to let her keep Mush....