I didn't actually mean that it would take extra effort to move the center balance in a swagger walk, but that it moves at all. Optimally, Your center of balance remains constantly on your centerline and roughly at equal distance from your feet at all times,without any counterbalancing movement, when walking . If you walk with a pronounced hip sway such as the one in the game, it necessitates a more pronounced than normal counterbalancing movement from your head/upper body to the opposite direction due to simple physics.Its automatic and the person doing it wouldnt even notice it under normal circumstances. The effort i'm talking about comes from trying to maintain balance when its rocked for one reason or another.The optimal "warrior walk" is simply better prepared to counter the upsetting force as the body has much fewer balance degrading motions to contend with and has wider foot placement than what a strut uses.
...And talks like this is why i love BSN 
The only way that would be applicable is if you're ambushed and unprepared for battle, even then, if you had training, you'd recover quickly. Say you're just casually walking along with your companions, bantering, checking out your LI's butt, or simply going from point A to B, when suddenly you spot enemies ahead, or they begin an attack. You'd no longer be in "walk mode". You would then take on a fighter's stance. Your feet would spread , aligning with your shoulders, one foot slightly behind the other-- all to prepare for any upsetting balance, much like a shooter's pose to avoid the kickback from unbalancing you. You would approach your enemy with deliberate movements, both offensive and defensive. None of that would have anything to do with your gait because they would be independent of each other. Same for sneaking. If you were tracking, hunting, trying to remain undetected or following someone, you wouldn't be walking to do so. Your stance would change to reflect your actions. Walking, sneaking and combat are all different movements and the two latter ones would need specific training and practice. The former, not really. It may change from your previous gait simply because of muscle change or because your posture changed, but that isn't necessarily the case.
There isn't a need to be technical really. I don't want to be that girl, but it is a fantasy setting and you're going to find things that are added, misused or tweaked simply because of artistic license and nothing to do with being historically accurate. There are inaccuracies with both armor and weapons, with combat movements and even injuries. That is to be expected because if those things were historically accurate, the game would be over before it really started and combat would be borderline boring, if not fully. A way a protagonist walks need not be anatomically or historically accurate because, and especially for a character created, it isn't so much about being accurate, but more about being pleasing to the eye. I guess what I am trying to say is there is no real reason why she can't or couldn't walk the way she does, except that people dislike the way it looks. Which is completely valid, don't get me wrong--but using historical or physical excuses for why she can't is just grasping at straws, and not very sturdy ones.
The problem with making a feature like that "pleasing", is that you can't please everyone. Had the animations been the same as male, I can guarantee threads would have popped up with complaints about her walk being too masculine, much like, but opposite to this thread. Had they made them neutral, people would have complained that the female didn't have her very own animations. I think with making a separate animation for the female--which a lot of people wanted-- they just fell a bit. Personally, I think they should have took their chances with something neutral. Some would complain, but in the end, it would have been a fair and even tilt and would have fit with any personality trait or class. Hopefully next time, they will do so.