In the first two Mass Effect games I gave my Shepard the ponytail hair, and I noticed that rather than being tied up with a hairband, her ponytail was just tied up with... more hair. I thought her hair, when loose, must be really long! It's no wonder she keeps it tied back for her military excursions. Here she is with a slightly more relaxed style.
For her face I used screenshots of my in-game Shepard as a reference. For her pose I used Jennifer Hale, Shepard's voice actress, in this video
. (If I am half as good looking as Jennifer Hale when I'm her age, I will be very happy indeed. And her musculature makes a relatively convincing reference even for an action girl like Shepard. What a lady!)