This is wonderful and also very hard to write a critique on since some of the "sloppiness" in fact adds to the style. with that said I do think that pointing at problems with a piece of art is one of the best ways to help some one improve it.
ALSO this is all just my point of veiw.
First of all i think that you need to work on lining thickness a little bit the nose seems really fine and sharp yet the hears are wide and smoother and the neck and cheeks almost have no line art at all. its not that any of those are bad its just that it jumps from one to the other.
Her eye say that she is very happy and playful with the one wide eye and the happy wink.; however, the face is pulled back and the chin is lowered this is a really minor detail but that's more of a defensive pose. yet again she maybe play fighting or teasing.
The far ear seems to be almost detached from the head. you can tell because on the first eye around half of it is attached to the head while on the other side the bottom 1/4 is hidden and because of the angle even less of it would be attached.
The last thing is the only one that really has to do with style and its just that I think you end the neck very suddenly for being such a loose light hearted drawing. I would hint at more of a body.