WOW in love :D
I feel that the most important parts of any girl illustration are the eyes and the hair. You completely nailed both.
The bamboo background looks great in this picture too, contrasts nicely with her red theme.
One personal problem I have with this picture is the lack of evidence that she's a ninja. No offense, but she could easily pass for a stripper at some nude bar. (Kinky yum) But again, its a personal thing.