Here I have lain construction lines over her face to show what I mean. The vertical line establishes the center of her face. She's looking squarely at the "camera"; the line runs from the point of her chin, through her nose, and between her eyes.
The upper horizontal line is the "eye line", of course, which also establishes the location of her cheekbones. The lower one is the "mouth line"; I placed it slightly askew--the right side is a few pixels higher than it should be, and the line should be parallel with the eye line--but it's close enough to show how "off" the light blue line is, which connects the sides of her jawbones.
Ideally the light blue line should be congruent with the mouth line, but it isn't. Looking at the triangle made by the ouline of her jaw and the mouth line, you can see how the right side of the image doesn't match the left side.
What is really interesting about all this is that nine times out of ten this kind of error will escape notice, and in the larger scheme of things really it doesn't matter at all.
I've been drawing (or trying to draw) comics, seriously, for 12 years, and in that time I like to think I've learned a little bit about how to draw. And I've learned that yes, there are things I see in comic art that other people don't notice--because by drawing so much I have learned what and how and why, at least to some small extent.
Usually, if I point out such errors in my own work to non-artists, they will tell me, "I wouldn't have noticed that if you hadn't pointed it out to me." The fact is, I only happened to notice the asymmetry of Mara's face while looking over that entry, because the image wasn't moving. Particularly in anime, individual drawings are less important compared with how they look when animated.
It is possible that the asymmetry was deliberate, in fact; I can think of several reasons why the artists might have deliberatey introduced such an asymmetry into the image. The fact that one tends not to notice it does not mean that it has no purpose.
Considering how much Belldandy's face varies from scene to scene--and that is very noticeable, by the way!--it's not surprising that other characters are similarly inconsistent. Belldandy's artwork is the single largest sticking point I have with the O!MG! TV series; even the stupid fansub romaji "Marller" crap is nothing compared with that.