This isn't about phasing a ten-mile long and two-mile wide bullet of alien metal. That's actually simple enough. I mean, this IS a comic book.
No...I mean when did she gain the ability to phase without having to breath. She couldn't phase through that much metal - or for that matter, that much of anything solid - on a single breath. I'm going to suggest that she may have learned to sift breathable oxygen from matter as she passes through it. But...is this an ability she had before Joss wrote her?
Also, she'd aparently learned a REALLY coot trick where she could keep herself in phase while unphasing one part of her (punching Emma in the face while the rest of her body was still phased), and I have no problem with that. I mean, powers evolve. I can easily imagine her learning how to do this sort of stuff.
But does anyone know WHEN she learned it? Or, was it just all Joss? Did Joss evolve her powers, or did he just not understand them?