That is one awesome sketch of a head I'm pretty inexperienced when it comes to critiquing so sorry if I point out something that is completely irrelevant, I need to start somewhere I guess :L

Anyway on the drawing above the head sketch (done with the tablet i'm sure) all I can suggest is that maybe where you've made the legs join with the torso is a little bit to high and maybe should be lowered a bit so where they meet isn't hidden by the jumper she is wearing. If I need to elaborate please let me know

Oh and on a side note is it hard getting used to a tablet?