I read a book about a guy who is the sole survivor of his planet. Everyone else was turned into a tree because of spores from some plants of that planet. There was a girl who believes her mother is dead, but instead her mother is a being who has existed from the creation of the world. Their house could travel at the speed of light. They use it once and the mother says that the travel could have broken the moon in half. The key to the machine that lets the house fly is a locket in the shape of a heart inside which there is a picture of the girl and the mother.
That sounds like Larklight by Philip Reeve (amazon). The girl also has a brother who is involved. They are fighting spiders who have existed in the solar system since it was formed (by the mother, using the house to coalesce all the matter). The boy who survived the tree plague is now a pirate captain.