Actually all lapis had to do was find a colonized planet with a functioning Galaxy warp. She didn't have to fly the whole way. Since it's implied Homeworld might've colonized most of our solar system or the planets past the asteroid belt then she'd probably have to go to Jupiter and then say her predicament and go back. Maybe each gem planet is different but some of them could be hallowed out based upon the core. Like how the core of some planets are gas then maybe they don't do it.