Her neck is too small, Terley. Instead of having about the width of her smile, the neck should almost reach as wide as the sides of her jaw.
I don't like the generic star on her cheek compared to the better looking twinkles. Also, you've got very rich dark shades, but very pale light ones. Add more saturation or change the lighter colors completely to add more interest.
Her nose is segemnted so as too look stuck on, ease the transition from the straight line of darker colors on the left side of the bridge of her nose.
Her smile is wide, but her cheeks dont match up. There should be a large dark crease on the right side and a matching highlight with a bit of dark on the left.
Good job thus far. Please detail her hair, this is looking alarmingly like your avatar which always seemed unfinished for lack of detailed hair. Look at other pixel artist portraiture, and see how highlights can really make hair pop.