They're being evil and they haven't told us yet. But Illyria turned into her in the last panel of Issue 5.

Of course, Issue 6 is going off on some wild tangent. We won't find out for at least another three months... *cries*

You might be able to get them through Amazon. If not there, TFAW will have them, or even IDW. Maybe wait for the trade, which I'd think would be coming out soonish.