I don't remember any Shepard being ballerina though, I'm quite sure they were all soldiers.
In what kind of world a soldier can't be a ballerina? Given how many girls practiced ballet I'm guessing at least 10% of real life female soldiers were ballerinas at some point in their lives. But thats not even an issue, she could have started after becoming a soldier. Or just be posing to lure an attractive male. It doesn't matter. It should be our options and our choices, and posters should be ignored since as I said, it is impossible to fit the subjective fantasy of millions of players into one image, some people will love, some people will hate. no matter what they do.
Edit: At animations, considering how 3D is handled by engines, there should be 3 animations for the player to select, female (stereotypical), male (stereotypical), neutral (realistic) - one extra type of animation would not be that hard to do.