Drake had likely flied in dragon shape
Chii... ok uhm... made a boat from her pink mass XD

perhaps there was some kind of boat going to Genosha, a supply boat the 2 stowed, well Drake might not be a stowaway, but Chii would at least knowing her XD

oh, if Drake used his megamorph to fly, she might have used her mass to attached herself on his tail, then he wont notice her XD