It's a girl. On the original comic SPOILERRRRRRSSS lastest page has this girl, and she has a feminine figure (dat full package), a dress and face looks quiet girly. Smartpants, this ain't even a yaoi manga so chances are so dim anyway.
Well, the person on the right is quite androgynous. Their gender isn't hinted at in any way. They assume female because of the long hair and possibly the way the person is positioned. One might assume male because Snippy has always been known to us as male and we assume that the person is Snippy since they're looking at the mask. tl;dr it's impossible to tell ;3