I find it extremely amusing that people are fixating on her top. The traffic I've gotten from the underboobs section of tvtropes alone is worth it, but here's the skinny on her skimpy top.
X's top is made of a material called "Smart Fabric". It is a high tech textile that can temporarily bond to the skin (or other organic surfaces). It's like its sticky without being sticky. When its bonded, it also gains a certain amount of rigidity, allowing it to hold its shape to some degree. The shape it takes is the shape its draped over/adhered to. So when X put her top on, she just had to position it, activate the shirt, and its now stuck and supportive. No matter how much she bounces, the shirt will not come loose or let any naughty bits pop out. Unlike conventional sticky stuff, it will not let go of her skin until the shirt is turned off. The rigidity of the shirt is such that it allows for some movement, but not so much that it would hurt. Much like a conventional bra, but instead of being supported from the bottom, its supported from the top.
This is a creation of fashion in the Shifters Universe. It is important to note that while fashion can be practical, often the more high end fashion is anything but. Part of her outfit is to poke fun at those who follow the tenant of fashion over practicality.
Just attempting to stir some discussion here.