Okay I know this is a just a line sketch. The hair looks fine. The rest of it seems out of proportion (ie the ears are too small,the arm that crosses over seems detached the upper arm in the foreground looks too big for her body and the fingers look flat as they grasp the arm).

In your drawing classes, has you professor gone over facial proportions? You have a neat style in how you draw your faces, but on some of your drawings, and in this one, some of the facial features don't match up. The eye on the right is lower, the nose and the mouth are both a bit to high up and her chin is a little too long.

I don't know if you already have a copy for school, but there is a really good art reference book called "Drawing the Human Head". If you haven't started already,it's good to have a bunch of reference books in your personal library. I like to scout out the bargain section at B&N and Borders plus used book stores a lot to see if the have anything useful for whatever I am working on.

I hope this helps.