Well, i think this is how it happened: The alien queen produced an egg inside her, unfinished, like a slimy mess or something which would later evolve. While she was on the shuttle, she spit this slimy mess right onto the wall, where it evolved. I mean, why not? Alien can spit acid out of their bodies, why not queens eggs? The facehugger that got the dog just ran by and got onto the shuttle with the queen. Thats plausible and logic.
I mean, think about it: They landed in a HIVE of aliens. Of course something for onboard.