The Rat Queen

Three refugees from a doomed planet, thrown together on an empty spaceship during a botched evacuation: a young man named Elton, a baby girl whom he names Becky, and a rat. With no one on board who can pilot the ship, it simply speeds onward on "auto", at less than the speed of light to nowhere, until they’re captured by galactic beings hostile to humanity. Elton, is kept prisoner and joins other humans being held on their space station, while Becky escapes into the ventilation shafts, and grows up feral, thinking she’s a rat. She smells like a rat, squeaks like a rat, and though she is rather large, the other rats think she’s a rat.

A family of orphans, a girl and two younger boys, have also managed to stay undetected by the Galactics, surviving in an empty section of the space station. They find Becky, and adopt her into their “family”.

The galactic non-human nations have become fed up with humanity, and have made it illegal for them to travel outside their own solar systems. Some would prefer they become extinct, and they have the means to accomplish that.

Things especially look bad for the humans being held on the space station until they are sent to resettle a vacant planet that had been abandoned by the previous human population. There was a reason it was abandoned, and the humans aren’t expected to survive.

But the little girl who thinks she’s a rat is the key to the survival of humanity.