Does anyone else get the feeling that Elsie might have already been horrifically killed by someone on her ship, perhaps long before she even appeared, and what we're seeing of her is her remains being controlled? Quite possibly that shady bowl-cut guy seen on the first character group art and in Chapter 3? Clearly something is meant to be off about this whole pirate encounter. Not just why her face suddenly changed, but why the halls are covered in slime and eggs, and why the crew has become a bunch of parasite-infected zombies.
I really don't want to be a party pooper about how awesome and terrifying she looks, or how she came to look like that. This could just as easily lead to interesting stuff, but this wouldn't the first time Hiro brought down a powerful and promising enemy hardly anyone knows just to prove the might of another, stronger one (and no, FT didn't start his trend of doing this). Maybe he cooked up her whole character for the purpose of hooking readers into new, decidedly non-FT things. Or maybe he can't imagine someone who looks like Erza being evil (without a "good" Erza to counterbalance it), and thus gave her a new face to distance her from a familiar one.
Either way, I'm suddenly feeling uneasy about this. But the next chapter title is the same as the series title, meaning the whole encounter with Elsie could either tie into what this story is all about, or get easily brushed aside by it. Given her whole familiarity with Shiki, I'm really hoping for the former.