From perona looking down at Zoro, I have to admit that she is floating, and therefore in ghost form.
But them going down to fishman island without introducing her as a new member is bad storytelling. At this point, Perona has as much a chance as the Kuja pirates, heracles'n, Rayleigh, the okamas, the weather-wizards and the bird of joining the crew.
At this point, she is just being used as a plot device to hold off the marines (along with the others' aides).
Also, she is surprised that the Strahats are "still putzing around" the island, which is clear that her body is not on the ship, because if it is, she would've known that they weren't on the ship yet.
Check and mate, Perona theorists.