The only important face feature are the eyes imho. Look at old NES graphics. As long as a sprite has eyes, it looks like a lifeform. But if it misses the eyes... lifeless. And who's interested in mouth and nose (well, nose is ok) at this size? Study NES graphics (Zelda 1 e.g.)
Look at the sprite-rips Arne
made here. They look more lively with one color than your full color sprite. Why not give her a feature (like a gun) or a more dynamic stance. The small sprites prove that it's possible at this size.
And don't forget.. if you have a 8-headed person in foreshortening from top view, slightly tilted, the head could be half of the size of the sprite! Maybe you should set the overall perspective first and do the sprites afterwards. It looks like you're using a frontview currently (compared with the other thread (btw, why did you open a new thread? anyway). But if you have a shoulder-width with two heads, it mostly looks like men and not female, if you don't hightlight her hips more.
Here's a small doodle to show what I meant
PS: And please post just 100% pictures, we have a zoom-script here. If you wish to post it in another forum, feel free to upload another version (200%), but we have to resize you sprites to analyse and edit them.