48 pixels is large enough that you can use references. Here are a few to look at to get you started. You probably want to find ones closer to your vision of this character than these, though.
The first is a model from
http://www.female-anatomy-for-artist.com/. Heavier bones and blunter features than what you're drawing, but the head and features are in roughly the same position, and the hair might work for you.
The second is cropped from The Martyr of the Solway by John Everett Millais, painted in 1871. Image from
http://www.artrenewal.org. It's not a good match for your image, but I like to study the oil painters for style and shading, particularly the skin tones.
The last is from a dollz site,
http://pixel.monicang.com/dolls.php. Not pixel art, but dollz do have nice hair.
In general, maybe more face and less hair. I recommend against dithering.
Hope this helps,
Tourist
