I agree with Taragreen - armor does blur gender lines. Besides, you have given Zura more of a suggestion of hips, and there's something about the face that makes me think "of course this is girl!Zuko" - maybe it's just something softer, or how the phoenix tail looks more like a ponytail or something from this angle.

In conclusion... Zura = awesome (why do I love it so much when characters are maternal/paternal/parental?), and I look forward to more stuff in the Sun Child universe! :D